test_http_server.cc - SHIFTPHONES/android_system_update_engine - Gitiles

 // Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 // This file implements a simple HTTP server. It can exhibit odd behavior
 // that's useful for testing. For example, it's useful to test that
 // the updater can continue a connection if it's dropped, or that it
 // handles very slow data transfers.

 // To use this, simply make an HTTP connection to localhost:port and
 // GET a url.

 #include <errno.h>
 #include <inttypes.h>
 #include <netinet/in.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <unistd.h>

 #include <algorithm>
 #include <string>
 #include <vector>

 #include <base/logging.h>
 #include <base/string_split.h>
 #include <base/string_util.h>
 #include <base/stringprintf.h>

 #include "update_engine/http_common.h"
 #include "update_engine/http_fetcher_unittest.h"


 // HTTP end-of-line delimiter; sorry, this needs to be a macro.
 #define EOL "\r\n"

 using std::min;
 using std::string;
 using std::vector;


 namespace chromeos_update_engine {

 struct HttpRequest {
   HttpRequest()
       : start_offset(0), end_offset(0), return_code(kHttpResponseOk) {}
   string host;
   string url;
   off_t start_offset;
   off_t end_offset;  // non-inclusive, zero indicates unspecified.
   HttpResponseCode return_code;
 };

 bool ParseRequest(int fd, HttpRequest* request) {
   string headers;
   do {
     char buf[1024];
     ssize_t r = read(fd, buf, sizeof(buf));
     if (r < 0) {
       perror("read");
       exit(1);
     }
     headers.append(buf, r);
   } while (!EndsWith(headers, EOL EOL, true));

   LOG(INFO) << "got headers:\n--8<------8<------8<------8<----\n"
             << headers
             << "\n--8<------8<------8<------8<----";

   // Break header into lines.
   std::vector<string> lines;
   base::SplitStringUsingSubstr(
       headers.substr(0, headers.length() - strlen(EOL EOL)), EOL, &lines);

   // Decode URL line.
   std::vector<string> terms;
   base::SplitStringAlongWhitespace(lines[0], &terms);
   CHECK_EQ(terms.size(), static_cast<vector<string>::size_type>(3));
   CHECK_EQ(terms[0], "GET");
   request->url = terms[1];
   LOG(INFO) << "URL: " << request->url;

   // Decode remaining lines.
   size_t i;
   for (i = 1; i < lines.size(); i++) {
     std::vector<string> terms;
     base::SplitStringAlongWhitespace(lines[i], &terms);

     if (terms[0] == "Range:") {
       CHECK_EQ(terms.size(), static_cast<vector<string>::size_type>(2));
       string &range = terms[1];
       LOG(INFO) << "range attribute: " << range;
       CHECK(StartsWithASCII(range, "bytes=", true) &&
             range.find('-') != string::npos);
       request->start_offset = atoll(range.c_str() + strlen("bytes="));
       // Decode end offset and increment it by one (so it is non-inclusive).
       if (range.find('-') < range.length() - 1)
         request->end_offset = atoll(range.c_str() + range.find('-') + 1) + 1;
       request->return_code = kHttpResponsePartialContent;
       std::string tmp_str = StringPrintf("decoded range offsets: start=%jd "
                                          "end=", request->start_offset);
       if (request->end_offset > 0)
         base::StringAppendF(&tmp_str, "%jd (non-inclusive)",
                             request->end_offset);
       else
         base::StringAppendF(&tmp_str, "unspecified");
       LOG(INFO) << tmp_str;
     } else if (terms[0] == "Host:") {
       CHECK_EQ(terms.size(), static_cast<vector<string>::size_type>(2));
       request->host = terms[1];
       LOG(INFO) << "host attribute: " << request->host;
     } else {
       LOG(WARNING) << "ignoring HTTP attribute: `" << lines[i] << "'";
     }
   }

   return true;
 }

 string Itoa(off_t num) {
   char buf[100] = {0};
   snprintf(buf, sizeof(buf), "%" PRIi64, num);
   return buf;
 }

 // Writes a string into a file. Returns total number of bytes written or -1 if a
 // write error occurred.
 ssize_t WriteString(int fd, const string& str) {
   const size_t total_size = str.size();
   size_t remaining_size = total_size;
   char const *data = str.data();

   while (remaining_size) {
     ssize_t written = write(fd, data, remaining_size);
     if (written < 0) {
       perror("write");
       LOG(INFO) << "write failed";
       return -1;
     }
     data += written;
     remaining_size -= written;
   }

   return total_size;
 }

 // Writes the headers of an HTTP response into a file.
 ssize_t WriteHeaders(int fd, const off_t start_offset, const off_t end_offset,
                      HttpResponseCode return_code) {
   ssize_t written = 0, ret;

   ret = WriteString(fd,
                     string("HTTP/1.1 ") + Itoa(return_code) + " " +
                     GetHttpResponseDescription(return_code) +
                     EOL
                     "Content-Type: application/octet-stream" EOL);
   if (ret < 0)
     return -1;
   written += ret;

   // Compute content legnth.
   const off_t content_length = end_offset - start_offset;;

   // A start offset that equals the end offset indicates that the response
   // should contain the full range of bytes in the requested resource.
   if (start_offset || start_offset == end_offset) {
     ret = WriteString(fd,
                       string("Accept-Ranges: bytes" EOL
                              "Content-Range: bytes ") +
                       Itoa(start_offset == end_offset ? 0 : start_offset) +
                       "-" + Itoa(end_offset - 1) + "/" + Itoa(end_offset) +
                       EOL);
     if (ret < 0)
       return -1;
     written += ret;
   }

   ret = WriteString(fd, string("Content-Length: ") + Itoa(content_length) +
                     EOL EOL);
   if (ret < 0)
     return -1;
   written += ret;

   return written;
 }

 // Writes a predetermined payload of lines of ascending bytes to a file. The
 // first byte of output is appropriately offset with respect to the request line
 // length.  Returns the number of successfully written bytes.
 size_t WritePayload(int fd, const off_t start_offset, const off_t end_offset,
                     const char first_byte, const size_t line_len) {
   CHECK_LE(start_offset, end_offset);
   CHECK_GT(line_len, static_cast<size_t>(0));

   LOG(INFO) << "writing payload: " << line_len << "-byte lines starting with `"
             << first_byte << "', offset range " << start_offset << " -> "
             << end_offset;

   // Populate line of ascending characters.
   string line;
   line.reserve(line_len);
   char byte = first_byte;
   size_t i;
   for (i = 0; i < line_len; i++)
     line += byte++;

   const size_t total_len = end_offset - start_offset;
   size_t remaining_len = total_len;
   bool success = true;

   // If start offset is not aligned with line boundary, output partial line up
   // to the first line boundary.
   size_t start_modulo = start_offset % line_len;
   if (start_modulo) {
     string partial = line.substr(start_modulo, remaining_len);
     ssize_t ret = WriteString(fd, partial);
     if ((success = (ret >= 0 && (size_t) ret == partial.length())))
       remaining_len -= partial.length();
   }

   // Output full lines up to the maximal line boundary below the end offset.
   while (success && remaining_len >= line_len) {
     ssize_t ret = WriteString(fd, line);
     if ((success = (ret >= 0 && (size_t) ret == line_len)))
       remaining_len -= line_len;
   }

   // Output a partial line up to the end offset.
   if (success && remaining_len) {
     string partial = line.substr(0, remaining_len);
     ssize_t ret = WriteString(fd, partial);
     if ((success = (ret >= 0 && (size_t) ret == partial.length())))
       remaining_len -= partial.length();
   }

   return (total_len - remaining_len);
 }

 // Write default payload lines of the form 'abcdefghij'.
 inline size_t WritePayload(int fd, const off_t start_offset,
                            const off_t end_offset) {
   return WritePayload(fd, start_offset, end_offset, 'a', 10);
 }

 // Send an empty response, then kill the server.
 void HandleQuit(int fd) {
   WriteHeaders(fd, 0, 0, kHttpResponseOk);
   LOG(INFO) << "pid(" << getpid() <<  "): HTTP server exiting ...";
   exit(0);
 }


 // Generates an HTTP response with payload corresponding to requested offsets
 // and length.  Optionally, truncate the payload at a given length and add a
 // pause midway through the transfer.  Returns the total number of bytes
 // delivered or -1 for error.
 ssize_t HandleGet(int fd, const HttpRequest& request, const size_t total_length,
                   const size_t truncate_length, const int sleep_every,
                   const int sleep_secs) {
   ssize_t ret;
   size_t written = 0;

   // Obtain start offset, make sure it is within total payload length.
   const size_t start_offset = request.start_offset;
   if (start_offset >= total_length) {
     LOG(WARNING) << "start offset (" << start_offset
                  << ") exceeds total length (" << total_length
                  << "), generating error response ("
                  << kHttpResponseReqRangeNotSat << ")";
     return WriteHeaders(fd, total_length, total_length,
                         kHttpResponseReqRangeNotSat);
   }

   // Obtain end offset, adjust to fit in total payload length and ensure it does
   // not preceded the start offset.
   size_t end_offset = (request.end_offset > 0 ?
                        request.end_offset : total_length);
   if (end_offset < start_offset) {
     LOG(WARNING) << "end offset (" << end_offset << ") precedes start offset ("
                  << start_offset << "), generating error response";
     return WriteHeaders(fd, 0, 0, kHttpResponseBadRequest);
   }
   if (end_offset > total_length) {
     LOG(INFO) << "requested end offset (" << end_offset
               << ") exceeds total length (" << total_length << "), adjusting";
     end_offset = total_length;
   }

   // Generate headers
   LOG(INFO) << "generating response header: range=" << start_offset << "-"
             << (end_offset - 1) << "/" << (end_offset - start_offset)
             << ", return code=" << request.return_code;
   if ((ret = WriteHeaders(fd, start_offset, end_offset,
                           request.return_code)) < 0)
     return -1;
   LOG(INFO) << ret << " header bytes written";
   written += ret;

   // Compute payload length, truncate as necessary.
   size_t payload_length = end_offset - start_offset;
   if (truncate_length > 0 && truncate_length < payload_length) {
     LOG(INFO) << "truncating request payload length (" << payload_length
               << ") at " << truncate_length;
     payload_length = truncate_length;
     end_offset = start_offset + payload_length;
   }

   LOG(INFO) << "generating response payload: range=" << start_offset << "-"
             << (end_offset - 1) << "/" << (end_offset - start_offset);

   // Decide about optional midway delay.
   if (truncate_length > 0 && sleep_every > 0 && sleep_secs >= 0 &&
       start_offset % (truncate_length * sleep_every) == 0) {
     const off_t midway_offset = start_offset + payload_length / 2;

     if ((ret = WritePayload(fd, start_offset, midway_offset)) < 0)
       return -1;
     LOG(INFO) << ret << " payload bytes written (first chunk)";
     written += ret;

     LOG(INFO) << "sleeping for " << sleep_secs << " seconds...";
     sleep(sleep_secs);

     if ((ret = WritePayload(fd, midway_offset, end_offset)) < 0)
       return -1;
     LOG(INFO) << ret << " payload bytes written (second chunk)";
     written += ret;
   } else {
     if ((ret = WritePayload(fd, start_offset, end_offset)) < 0)
       return -1;
     LOG(INFO) << ret << " payload bytes written";
     written += ret;
   }

   LOG(INFO) << "response generation complete, " << written
             << " total bytes written";
   return written;
 }

 ssize_t HandleGet(int fd, const HttpRequest& request,
                   const size_t total_length) {
   return HandleGet(fd, request, total_length, 0, 0, 0);
 }

 // Handles /redirect/<code>/<url> requests by returning the specified
 // redirect <code> with a location pointing to /<url>.
 void HandleRedirect(int fd, const HttpRequest& request) {
   LOG(INFO) << "Redirecting...";
   string url = request.url;
   CHECK_EQ(static_cast<size_t>(0), url.find("/redirect/"));
   url.erase(0, strlen("/redirect/"));
   string::size_type url_start = url.find('/');
   CHECK_NE(url_start, string::npos);
   HttpResponseCode code = StringToHttpResponseCode(url.c_str());
   url.erase(0, url_start);
   url = "http://" + request.host + url;
   const char *status = GetHttpResponseDescription(code);
   if (!status)
     CHECK(false) << "Unrecognized redirection code: " << code;
   LOG(INFO) << "Code: " << code << " " << status;
   LOG(INFO) << "New URL: " << url;

   ssize_t ret;
   if ((ret = WriteString(fd, "HTTP/1.1 " + Itoa(code) + " " +
                          status + EOL)) < 0)
     return;
   WriteString(fd, "Location: " + url + EOL);
 }

 // Generate a page not found error response with actual text payload. Return
 // number of bytes written or -1 for error.
 ssize_t HandleError(int fd, const HttpRequest& request) {
   LOG(INFO) << "Generating error HTTP response";

   ssize_t ret;
   size_t written = 0;

   const string data("This is an error page.");

   if ((ret = WriteHeaders(fd, 0, data.size(), kHttpResponseNotFound)) < 0)
     return -1;
   written += ret;

   if ((ret = WriteString(fd, data)) < 0)
     return -1;
   written += ret;

   return written;
 }

 // Generate an error response if the requested offset is nonzero, up to a given
 // maximal number of successive failures.  The error generated is an "Internal
 // Server Error" (500).
 ssize_t HandleErrorIfOffset(int fd, const HttpRequest& request,
                             size_t end_offset, int max_fails) {
   static int num_fails = 0;

   if (request.start_offset > 0 && num_fails < max_fails) {
     LOG(INFO) << "Generating error HTTP response";

     ssize_t ret;
     size_t written = 0;

     const string data("This is an error page.");

     if ((ret = WriteHeaders(fd, 0, data.size(),
                             kHttpResponseInternalServerError)) < 0)
       return -1;
     written += ret;

     if ((ret = WriteString(fd, data)) < 0)
       return -1;
     written += ret;

     num_fails++;
     return written;
   } else {
     num_fails = 0;
     return HandleGet(fd, request, end_offset);
   }
 }

 void HandleDefault(int fd, const HttpRequest& request) {
   const off_t start_offset = request.start_offset;
   const string data("unhandled path");
   const size_t size = data.size();
   ssize_t ret;

   if ((ret = WriteHeaders(fd, start_offset, size, request.return_code)) < 0)
     return;
   WriteString(fd, (start_offset < static_cast<off_t>(size) ?
                    data.substr(start_offset) : ""));
 }


 // Break a URL into terms delimited by slashes.
 class UrlTerms {
  public:
   UrlTerms(string &url, size_t num_terms) {
     // URL must be non-empty and start with a slash.
     CHECK_GT(url.size(), static_cast<size_t>(0));
     CHECK_EQ(url[0], '/');

     // Split it into terms delimited by slashes, omitting the preceeding slash.
     base::SplitStringDontTrim(url.substr(1), '/', &terms);

     // Ensure expected length.
     CHECK_EQ(terms.size(), num_terms);
   }

   inline string Get(const off_t index) const {
     return terms[index];
   }
   inline const char *GetCStr(const off_t index) const {
     return Get(index).c_str();
   }
   inline int GetInt(const off_t index) const {
     return atoi(GetCStr(index));
   }
   inline long GetLong(const off_t index) const {
     return atol(GetCStr(index));
   }

  private:
   std::vector<string> terms;
 };

 void HandleConnection(int fd) {
   HttpRequest request;
   ParseRequest(fd, &request);

   string &url = request.url;
   LOG(INFO) << "pid(" << getpid() <<  "): handling url " << url;
   if (url == "/quitquitquit") {
     HandleQuit(fd);
   } else if (StartsWithASCII(url, "/download/", true)) {
     const UrlTerms terms(url, 2);
     HandleGet(fd, request, terms.GetLong(1));
   } else if (StartsWithASCII(url, "/flaky/", true)) {
     const UrlTerms terms(url, 5);
     HandleGet(fd, request, terms.GetLong(1), terms.GetLong(2), terms.GetLong(3),
               terms.GetLong(4));
   } else if (url.find("/redirect/") == 0) {
     HandleRedirect(fd, request);
   } else if (url == "/error") {
     HandleError(fd, request);
   } else if (StartsWithASCII(url, "/error-if-offset/", true)) {
     const UrlTerms terms(url, 3);
     HandleErrorIfOffset(fd, request, terms.GetLong(1), terms.GetInt(2));
   } else {
     HandleDefault(fd, request);
   }

   close(fd);
 }

 }  // namespace chromeos_update_engine

 using namespace chromeos_update_engine;

 int main(int argc, char** argv) {
   // Ignore SIGPIPE on write() to sockets.
   signal(SIGPIPE, SIG_IGN);

   socklen_t clilen;
   struct sockaddr_in server_addr;
   struct sockaddr_in client_addr;
   memset(&server_addr, 0, sizeof(server_addr));
   memset(&client_addr, 0, sizeof(client_addr));

   int listen_fd = socket(AF_INET, SOCK_STREAM, 0);
   if (listen_fd < 0)
     LOG(FATAL) << "socket() failed";

   server_addr.sin_family = AF_INET;
   server_addr.sin_addr.s_addr = INADDR_ANY;
   server_addr.sin_port = htons(kServerPort);

   {
     // Get rid of "Address in use" error
     int tr = 1;
     if (setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &tr,
                    sizeof(int)) == -1) {
       perror("setsockopt");
       exit(2);
     }
   }

   if (bind(listen_fd, reinterpret_cast<struct sockaddr *>(&server_addr),
            sizeof(server_addr)) < 0) {
     perror("bind");
     exit(3);
   }
   CHECK_EQ(listen(listen_fd,5), 0);
   while (1) {
     LOG(INFO) << "pid(" << getpid() <<  "): waiting to accept new connection";
     clilen = sizeof(client_addr);
     int client_fd = accept(listen_fd,
                            (struct sockaddr *) &client_addr,
                            &clilen);
     LOG(INFO) << "got past accept";
     if (client_fd < 0)
       LOG(FATAL) << "ERROR on accept";
     HandleConnection(client_fd);
   }
   return 0;
 }
	// Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	// This file implements a simple HTTP server. It can exhibit odd behavior
	// that's useful for testing. For example, it's useful to test that
	// the updater can continue a connection if it's dropped, or that it
	// handles very slow data transfers.

	// To use this, simply make an HTTP connection to localhost:port and
	// GET a url.

	#include <errno.h>
	#include <inttypes.h>
	#include <netinet/in.h>
	#include <signal.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/socket.h>
	#include <sys/types.h>
	#include <unistd.h>

	#include <algorithm>
	#include <string>
	#include <vector>

	#include <base/logging.h>
	#include <base/string_split.h>
	#include <base/string_util.h>
	#include <base/stringprintf.h>

	#include "update_engine/http_common.h"
	#include "update_engine/http_fetcher_unittest.h"


	// HTTP end-of-line delimiter; sorry, this needs to be a macro.
	#define EOL "\r\n"

	using std::min;
	using std::string;
	using std::vector;


	namespace chromeos_update_engine {

	struct HttpRequest {
	HttpRequest()
	: start_offset(0), end_offset(0), return_code(kHttpResponseOk) {}
	string host;
	string url;
	off_t start_offset;
	off_t end_offset; // non-inclusive, zero indicates unspecified.
	HttpResponseCode return_code;
	};

	bool ParseRequest(int fd, HttpRequest* request) {
	string headers;
	do {
	char buf[1024];
	ssize_t r = read(fd, buf, sizeof(buf));
	if (r < 0) {
	perror("read");
	exit(1);
	}
	headers.append(buf, r);
	} while (!EndsWith(headers, EOL EOL, true));

	LOG(INFO) << "got headers:\n--8<------8<------8<------8<----\n"
	<< headers
	<< "\n--8<------8<------8<------8<----";

	// Break header into lines.
	std::vector<string> lines;
	base::SplitStringUsingSubstr(
	headers.substr(0, headers.length() - strlen(EOL EOL)), EOL, &lines);

	// Decode URL line.
	std::vector<string> terms;
	base::SplitStringAlongWhitespace(lines[0], &terms);
	CHECK_EQ(terms.size(), static_cast<vector<string>::size_type>(3));
	CHECK_EQ(terms[0], "GET");
	request->url = terms[1];
	LOG(INFO) << "URL: " << request->url;

	// Decode remaining lines.
	size_t i;
	for (i = 1; i < lines.size(); i++) {
	std::vector<string> terms;
	base::SplitStringAlongWhitespace(lines[i], &terms);

	if (terms[0] == "Range:") {
	CHECK_EQ(terms.size(), static_cast<vector<string>::size_type>(2));
	string &range = terms[1];
	LOG(INFO) << "range attribute: " << range;
	CHECK(StartsWithASCII(range, "bytes=", true) &&
	range.find('-') != string::npos);
	request->start_offset = atoll(range.c_str() + strlen("bytes="));
	// Decode end offset and increment it by one (so it is non-inclusive).
	if (range.find('-') < range.length() - 1)
	request->end_offset = atoll(range.c_str() + range.find('-') + 1) + 1;
	request->return_code = kHttpResponsePartialContent;
	std::string tmp_str = StringPrintf("decoded range offsets: start=%jd "
	"end=", request->start_offset);
	if (request->end_offset > 0)
	base::StringAppendF(&tmp_str, "%jd (non-inclusive)",
	request->end_offset);
	else
	base::StringAppendF(&tmp_str, "unspecified");
	LOG(INFO) << tmp_str;
	} else if (terms[0] == "Host:") {
	CHECK_EQ(terms.size(), static_cast<vector<string>::size_type>(2));
	request->host = terms[1];
	LOG(INFO) << "host attribute: " << request->host;
	} else {
	LOG(WARNING) << "ignoring HTTP attribute: `" << lines[i] << "'";
	}
	}

	return true;
	}

	string Itoa(off_t num) {
	char buf[100] = {0};
	snprintf(buf, sizeof(buf), "%" PRIi64, num);
	return buf;
	}

	// Writes a string into a file. Returns total number of bytes written or -1 if a
	// write error occurred.
	ssize_t WriteString(int fd, const string& str) {
	const size_t total_size = str.size();
	size_t remaining_size = total_size;
	char const *data = str.data();

	while (remaining_size) {
	ssize_t written = write(fd, data, remaining_size);
	if (written < 0) {
	perror("write");
	LOG(INFO) << "write failed";
	return -1;
	}
	data += written;
	remaining_size -= written;
	}

	return total_size;
	}

	// Writes the headers of an HTTP response into a file.
	ssize_t WriteHeaders(int fd, const off_t start_offset, const off_t end_offset,
	HttpResponseCode return_code) {
	ssize_t written = 0, ret;

	ret = WriteString(fd,
	string("HTTP/1.1 ") + Itoa(return_code) + " " +
	GetHttpResponseDescription(return_code) +
	EOL
	"Content-Type: application/octet-stream" EOL);
	if (ret < 0)
	return -1;
	written += ret;

	// Compute content legnth.
	const off_t content_length = end_offset - start_offset;;

	// A start offset that equals the end offset indicates that the response
	// should contain the full range of bytes in the requested resource.
	if (start_offset \|\| start_offset == end_offset) {
	ret = WriteString(fd,
	string("Accept-Ranges: bytes" EOL
	"Content-Range: bytes ") +
	Itoa(start_offset == end_offset ? 0 : start_offset) +
	"-" + Itoa(end_offset - 1) + "/" + Itoa(end_offset) +
	EOL);
	if (ret < 0)
	return -1;
	written += ret;
	}

	ret = WriteString(fd, string("Content-Length: ") + Itoa(content_length) +
	EOL EOL);
	if (ret < 0)
	return -1;
	written += ret;

	return written;
	}

	// Writes a predetermined payload of lines of ascending bytes to a file. The
	// first byte of output is appropriately offset with respect to the request line
	// length. Returns the number of successfully written bytes.
	size_t WritePayload(int fd, const off_t start_offset, const off_t end_offset,
	const char first_byte, const size_t line_len) {
	CHECK_LE(start_offset, end_offset);
	CHECK_GT(line_len, static_cast<size_t>(0));

	LOG(INFO) << "writing payload: " << line_len << "-byte lines starting with `"
	<< first_byte << "', offset range " << start_offset << " -> "
	<< end_offset;

	// Populate line of ascending characters.
	string line;
	line.reserve(line_len);
	char byte = first_byte;
	size_t i;
	for (i = 0; i < line_len; i++)
	line += byte++;

	const size_t total_len = end_offset - start_offset;
	size_t remaining_len = total_len;
	bool success = true;

	// If start offset is not aligned with line boundary, output partial line up
	// to the first line boundary.
	size_t start_modulo = start_offset % line_len;
	if (start_modulo) {
	string partial = line.substr(start_modulo, remaining_len);
	ssize_t ret = WriteString(fd, partial);
	if ((success = (ret >= 0 && (size_t) ret == partial.length())))
	remaining_len -= partial.length();
	}

	// Output full lines up to the maximal line boundary below the end offset.
	while (success && remaining_len >= line_len) {
	ssize_t ret = WriteString(fd, line);
	if ((success = (ret >= 0 && (size_t) ret == line_len)))
	remaining_len -= line_len;
	}

	// Output a partial line up to the end offset.
	if (success && remaining_len) {
	string partial = line.substr(0, remaining_len);
	ssize_t ret = WriteString(fd, partial);
	if ((success = (ret >= 0 && (size_t) ret == partial.length())))
	remaining_len -= partial.length();
	}

	return (total_len - remaining_len);
	}

	// Write default payload lines of the form 'abcdefghij'.
	inline size_t WritePayload(int fd, const off_t start_offset,
	const off_t end_offset) {
	return WritePayload(fd, start_offset, end_offset, 'a', 10);
	}

	// Send an empty response, then kill the server.
	void HandleQuit(int fd) {
	WriteHeaders(fd, 0, 0, kHttpResponseOk);
	LOG(INFO) << "pid(" << getpid() << "): HTTP server exiting ...";
	exit(0);
	}


	// Generates an HTTP response with payload corresponding to requested offsets
	// and length. Optionally, truncate the payload at a given length and add a
	// pause midway through the transfer. Returns the total number of bytes
	// delivered or -1 for error.
	ssize_t HandleGet(int fd, const HttpRequest& request, const size_t total_length,
	const size_t truncate_length, const int sleep_every,
	const int sleep_secs) {
	ssize_t ret;
	size_t written = 0;

	// Obtain start offset, make sure it is within total payload length.
	const size_t start_offset = request.start_offset;
	if (start_offset >= total_length) {
	LOG(WARNING) << "start offset (" << start_offset
	<< ") exceeds total length (" << total_length
	<< "), generating error response ("
	<< kHttpResponseReqRangeNotSat << ")";
	return WriteHeaders(fd, total_length, total_length,
	kHttpResponseReqRangeNotSat);
	}

	// Obtain end offset, adjust to fit in total payload length and ensure it does
	// not preceded the start offset.
	size_t end_offset = (request.end_offset > 0 ?
	request.end_offset : total_length);
	if (end_offset < start_offset) {
	LOG(WARNING) << "end offset (" << end_offset << ") precedes start offset ("
	<< start_offset << "), generating error response";
	return WriteHeaders(fd, 0, 0, kHttpResponseBadRequest);
	}
	if (end_offset > total_length) {
	LOG(INFO) << "requested end offset (" << end_offset
	<< ") exceeds total length (" << total_length << "), adjusting";
	end_offset = total_length;
	}

	// Generate headers
	LOG(INFO) << "generating response header: range=" << start_offset << "-"
	<< (end_offset - 1) << "/" << (end_offset - start_offset)
	<< ", return code=" << request.return_code;
	if ((ret = WriteHeaders(fd, start_offset, end_offset,
	request.return_code)) < 0)
	return -1;
	LOG(INFO) << ret << " header bytes written";
	written += ret;

	// Compute payload length, truncate as necessary.
	size_t payload_length = end_offset - start_offset;
	if (truncate_length > 0 && truncate_length < payload_length) {
	LOG(INFO) << "truncating request payload length (" << payload_length
	<< ") at " << truncate_length;
	payload_length = truncate_length;
	end_offset = start_offset + payload_length;
	}

	LOG(INFO) << "generating response payload: range=" << start_offset << "-"
	<< (end_offset - 1) << "/" << (end_offset - start_offset);

	// Decide about optional midway delay.
	if (truncate_length > 0 && sleep_every > 0 && sleep_secs >= 0 &&
	start_offset % (truncate_length * sleep_every) == 0) {
	const off_t midway_offset = start_offset + payload_length / 2;

	if ((ret = WritePayload(fd, start_offset, midway_offset)) < 0)
	return -1;
	LOG(INFO) << ret << " payload bytes written (first chunk)";
	written += ret;

	LOG(INFO) << "sleeping for " << sleep_secs << " seconds...";
	sleep(sleep_secs);

	if ((ret = WritePayload(fd, midway_offset, end_offset)) < 0)
	return -1;
	LOG(INFO) << ret << " payload bytes written (second chunk)";
	written += ret;
	} else {
	if ((ret = WritePayload(fd, start_offset, end_offset)) < 0)
	return -1;
	LOG(INFO) << ret << " payload bytes written";
	written += ret;
	}

	LOG(INFO) << "response generation complete, " << written
	<< " total bytes written";
	return written;
	}

	ssize_t HandleGet(int fd, const HttpRequest& request,
	const size_t total_length) {
	return HandleGet(fd, request, total_length, 0, 0, 0);
	}

	// Handles /redirect/<code>/<url> requests by returning the specified
	// redirect <code> with a location pointing to /<url>.
	void HandleRedirect(int fd, const HttpRequest& request) {
	LOG(INFO) << "Redirecting...";
	string url = request.url;
	CHECK_EQ(static_cast<size_t>(0), url.find("/redirect/"));
	url.erase(0, strlen("/redirect/"));
	string::size_type url_start = url.find('/');
	CHECK_NE(url_start, string::npos);
	HttpResponseCode code = StringToHttpResponseCode(url.c_str());
	url.erase(0, url_start);
	url = "http://" + request.host + url;
	const char *status = GetHttpResponseDescription(code);
	if (!status)
	CHECK(false) << "Unrecognized redirection code: " << code;
	LOG(INFO) << "Code: " << code << " " << status;
	LOG(INFO) << "New URL: " << url;

	ssize_t ret;
	if ((ret = WriteString(fd, "HTTP/1.1 " + Itoa(code) + " " +
	status + EOL)) < 0)
	return;
	WriteString(fd, "Location: " + url + EOL);
	}

	// Generate a page not found error response with actual text payload. Return
	// number of bytes written or -1 for error.
	ssize_t HandleError(int fd, const HttpRequest& request) {
	LOG(INFO) << "Generating error HTTP response";

	ssize_t ret;
	size_t written = 0;

	const string data("This is an error page.");

	if ((ret = WriteHeaders(fd, 0, data.size(), kHttpResponseNotFound)) < 0)
	return -1;
	written += ret;

	if ((ret = WriteString(fd, data)) < 0)
	return -1;
	written += ret;

	return written;
	}

	// Generate an error response if the requested offset is nonzero, up to a given
	// maximal number of successive failures. The error generated is an "Internal
	// Server Error" (500).
	ssize_t HandleErrorIfOffset(int fd, const HttpRequest& request,
	size_t end_offset, int max_fails) {
	static int num_fails = 0;

	if (request.start_offset > 0 && num_fails < max_fails) {
	LOG(INFO) << "Generating error HTTP response";

	ssize_t ret;
	size_t written = 0;

	const string data("This is an error page.");

	if ((ret = WriteHeaders(fd, 0, data.size(),
	kHttpResponseInternalServerError)) < 0)
	return -1;
	written += ret;

	if ((ret = WriteString(fd, data)) < 0)
	return -1;
	written += ret;

	num_fails++;
	return written;
	} else {
	num_fails = 0;
	return HandleGet(fd, request, end_offset);
	}
	}

	void HandleDefault(int fd, const HttpRequest& request) {
	const off_t start_offset = request.start_offset;
	const string data("unhandled path");
	const size_t size = data.size();
	ssize_t ret;

	if ((ret = WriteHeaders(fd, start_offset, size, request.return_code)) < 0)
	return;
	WriteString(fd, (start_offset < static_cast<off_t>(size) ?
	data.substr(start_offset) : ""));
	}


	// Break a URL into terms delimited by slashes.
	class UrlTerms {
	public:
	UrlTerms(string &url, size_t num_terms) {
	// URL must be non-empty and start with a slash.
	CHECK_GT(url.size(), static_cast<size_t>(0));
	CHECK_EQ(url[0], '/');

	// Split it into terms delimited by slashes, omitting the preceeding slash.
	base::SplitStringDontTrim(url.substr(1), '/', &terms);

	// Ensure expected length.
	CHECK_EQ(terms.size(), num_terms);
	}

	inline string Get(const off_t index) const {
	return terms[index];
	}
	inline const char *GetCStr(const off_t index) const {
	return Get(index).c_str();
	}
	inline int GetInt(const off_t index) const {
	return atoi(GetCStr(index));
	}
	inline long GetLong(const off_t index) const {
	return atol(GetCStr(index));
	}

	private:
	std::vector<string> terms;
	};

	void HandleConnection(int fd) {
	HttpRequest request;
	ParseRequest(fd, &request);

	string &url = request.url;
	LOG(INFO) << "pid(" << getpid() << "): handling url " << url;
	if (url == "/quitquitquit") {
	HandleQuit(fd);
	} else if (StartsWithASCII(url, "/download/", true)) {
	const UrlTerms terms(url, 2);
	HandleGet(fd, request, terms.GetLong(1));
	} else if (StartsWithASCII(url, "/flaky/", true)) {
	const UrlTerms terms(url, 5);
	HandleGet(fd, request, terms.GetLong(1), terms.GetLong(2), terms.GetLong(3),
	terms.GetLong(4));
	} else if (url.find("/redirect/") == 0) {
	HandleRedirect(fd, request);
	} else if (url == "/error") {
	HandleError(fd, request);
	} else if (StartsWithASCII(url, "/error-if-offset/", true)) {
	const UrlTerms terms(url, 3);
	HandleErrorIfOffset(fd, request, terms.GetLong(1), terms.GetInt(2));
	} else {
	HandleDefault(fd, request);
	}

	close(fd);
	}

	} // namespace chromeos_update_engine

	using namespace chromeos_update_engine;

	int main(int argc, char** argv) {
	// Ignore SIGPIPE on write() to sockets.
	signal(SIGPIPE, SIG_IGN);

	socklen_t clilen;
	struct sockaddr_in server_addr;
	struct sockaddr_in client_addr;
	memset(&server_addr, 0, sizeof(server_addr));
	memset(&client_addr, 0, sizeof(client_addr));

	int listen_fd = socket(AF_INET, SOCK_STREAM, 0);
	if (listen_fd < 0)
	LOG(FATAL) << "socket() failed";

	server_addr.sin_family = AF_INET;
	server_addr.sin_addr.s_addr = INADDR_ANY;
	server_addr.sin_port = htons(kServerPort);

	{
	// Get rid of "Address in use" error
	int tr = 1;
	if (setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &tr,
	sizeof(int)) == -1) {
	perror("setsockopt");
	exit(2);
	}
	}

	if (bind(listen_fd, reinterpret_cast<struct sockaddr *>(&server_addr),
	sizeof(server_addr)) < 0) {
	perror("bind");
	exit(3);
	}
	CHECK_EQ(listen(listen_fd,5), 0);
	while (1) {
	LOG(INFO) << "pid(" << getpid() << "): waiting to accept new connection";
	clilen = sizeof(client_addr);
	int client_fd = accept(listen_fd,
	(struct sockaddr *) &client_addr,
	&clilen);
	LOG(INFO) << "got past accept";
	if (client_fd < 0)
	LOG(FATAL) << "ERROR on accept";
	HandleConnection(client_fd);
	}
	return 0;
	}