Add config option to specify amount of parallel download streams

It includes pacman.conf new 'ParallelDownloads' option that
specifies how many concurrent downloads cURL starts in parallel.

Add alpm_option_set_parallel_downloads() ALPM function that
allows to set this config option programmatically.

Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>
Signed-off-by: Allan McRae <allan@archlinux.org>

doc/pacman.conf.5.asciidoc

@@ -209,6 +209,11 @@ Options
 	Disable defaults for low speed limit and timeout on downloads. Use this
 	if you have issues downloading files with proxy and/or security gateway.
 
+*ParallelDownloads*::
+	Specifies number of concurrent download streams. The value needs to be a
+	positive integer. If this config option is not set then only one download
+	stream is used (i.e. downloads happen sequentially).
+
 
 Repository Sections
 -------------------

etc/pacman.conf.in

@@ -35,6 +35,7 @@ Architecture = auto
 #TotalDownload
 CheckSpace
 #VerbosePkgLists
+ParallelDownloads = 5
 
 # PGP signature checking
 #SigLevel = Optional

lib/libalpm/alpm.h

@@ -903,6 +903,15 @@ int alpm_option_set_remote_file_siglevel(alpm_handle_t *handle, int level);
 
 int alpm_option_set_disable_dl_timeout(alpm_handle_t *handle, unsigned short disable_dl_timeout);
 
+/** Sets number of parallel streams to download database and package files.
+ * If the function is not called then the default value of '1' stream
+ * (i.e. sequential download) is used.
+ * @param handle the context handle
+ * @param num_streams number of parallel download streams
+ * @return 0 on success, -1 on error
+ */
+int alpm_option_set_parallel_downloads(alpm_handle_t *handle, unsigned int num_streams);
+
 /** @} */
 
 /** @addtogroup alpm_api_databases Database Functions

lib/libalpm/handle.c

@@ -856,3 +856,18 @@ int SYMEXPORT alpm_option_set_disable_dl_timeout(alpm_handle_t *handle,
 #endif
 	return 0;
 }
+
+int SYMEXPORT alpm_option_set_parallel_downloads(alpm_handle_t *handle,
+		unsigned int num_streams)
+{
+	CHECK_HANDLE(handle, return -1);
+#ifdef HAVE_LIBCURL
+	if(num_streams < 1) {
+		return -1;
+	}
+	handle->parallel_downloads = num_streams;
+#else
+	(void)num_streams; /* silence unused variable warnings */
+#endif
+	return 0;
+}

lib/libalpm/handle.h

@@ -61,6 +61,7 @@ struct __alpm_handle_t {
 	/* libcurl handle */
 	CURL *curl;             /* reusable curl_easy handle */
 	unsigned short disable_dl_timeout;
+	unsigned int parallel_downloads; /* number of download streams */
 #endif
 
 #ifdef HAVE_LIBGPGME

src/pacman/conf.c

@@ -114,6 +114,8 @@ config_t *config_new(void)
 		newconfig->remotefilesiglevel = ALPM_SIG_USE_DEFAULT;
 	}
 
+	/* by default use 1 download stream */
+	newconfig->parallel_downloads = 1;
 	newconfig->colstr.colon   = ":: ";
 	newconfig->colstr.title   = "";
 	newconfig->colstr.repo    = "";
@@ -404,6 +406,32 @@ int config_set_arch(const char *arch)
 	return 0;
 }
 
+/**
+ * Parse a string into long number. The input string has to be non-empty
+ * and represent a number that fits long type.
+ * @param value the string to parse
+ * @param result pointer to long where the final result will be stored.
+ *   This result is modified if the input string parsed successfully.
+ * @return 0 in case if value parsed successfully, 1 otherwise.
+ */
+static int parse_number(char *value, long *result) {
+	char *endptr;
+	long val;
+	int invalid;
+
+	errno = 0; /* To distinguish success/failure after call */
+	val = strtol(value, &endptr, 10);
+	invalid = (errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
+		|| (*endptr != '\0')
+		|| (endptr == value);
+
+	if(!invalid) {
+		*result = val;
+	}
+
+	return invalid;
+}
+
 /**
  * Parse a signature verification level line.
  * @param values the list of parsed option values
@@ -683,6 +711,33 @@ static int _parse_options(const char *key, char *value,
 				return 1;
 			}
 			FREELIST(values);
+		} else if(strcmp(key, "ParallelDownloads") == 0) {
+			long number;
+			int err;
+
+			err = parse_number(value, &number);
+			if(err) {
+				pm_printf(ALPM_LOG_WARNING,
+						_("config file %s, line %d: invalid value for '%s' : '%s'\n"),
+						file, linenum, "ParallelDownloads", value);
+				return 1;
+			}
+
+			if(number < 1) {
+				pm_printf(ALPM_LOG_WARNING,
+						_("config file %s, line %d: value for '%s' has to be positive : '%s'\n"),
+						file, linenum, "ParallelDownloads", value);
+				return 1;
+			}
+
+			if(number > INT_MAX) {
+				pm_printf(ALPM_LOG_WARNING,
+						_("config file %s, line %d: value for '%s' is too large : '%s'\n"),
+						file, linenum, "ParallelDownloads", value);
+				return 1;
+			}
+
+			config->parallel_downloads = number;
 		} else {
 			pm_printf(ALPM_LOG_WARNING,
 					_("config file %s, line %d: directive '%s' in section '%s' not recognized.\n"),
@@ -851,6 +906,7 @@ static int setup_libalpm(void)
 	alpm_option_set_noextracts(handle, config->noextract);
 
 	alpm_option_set_disable_dl_timeout(handle, config->disable_dl_timeout);
+	alpm_option_set_parallel_downloads(handle, config->parallel_downloads);
 
 	for(i = config->assumeinstalled; i; i = i->next) {
 		char *entry = i->data;

src/pacman/conf.h

@@ -116,6 +116,8 @@ typedef struct __config_t {
 	/* When downloading, display the amount downloaded, rate, ETA, and percent
 	 * downloaded of the total download list */
 	unsigned short totaldownload;
+	/* number of parallel download streams */
+	unsigned int parallel_downloads;
 	/* select -Sc behavior */
 	unsigned short cleanmethod;
 	alpm_list_t *holdpkg;