[spotify] Fix for "Premium account required" (issue #1474)

Sadly user-agent spoofing seems to be necessary after Spotify sunset of
libspotify. Apparently librespot is whitelisted.

src/inputs/librespot-c/README.md

@@ -1,3 +1,6 @@
+Limited C version of librespot. No Spotify Connect support. Library only. Used
+by [OwnTone](https://github.com/owntone/owntone-server).
+
 Build:
 - autoreconf -i && ./configure && make
 

src/inputs/librespot-c/src/connection.c

@@ -1033,6 +1033,9 @@ msg_make_client_response_encrypted(uint8_t *out, size_t out_len, struct sp_sessi
   ClientResponseEncrypted client_response = CLIENT_RESPONSE_ENCRYPTED__INIT;
   LoginCredentials login_credentials = LOGIN_CREDENTIALS__INIT;
   SystemInfo system_info = SYSTEM_INFO__INIT;
+  const char *client_name;
+  const char *client_version;
+  const char *client_build_id;
   char system_information_string[64];
   char version_string[64];
   ssize_t len;
@@ -1061,18 +1064,21 @@ msg_make_client_response_encrypted(uint8_t *out, size_t out_len, struct sp_sessi
   else
     return -1;
 
+  // Note that Spotify seems to have whitelisting of client_name
+  client_name = (sp_sysinfo.client_name[0] != '\0') ? sp_sysinfo.client_name : "librespot";
+  client_version = (sp_sysinfo.client_version[0] != '\0') ? sp_sysinfo.client_version : "000000";
+  client_build_id = (sp_sysinfo.client_build_id[0] != '\0') ? sp_sysinfo.client_build_id : "0";
+  snprintf(system_information_string, sizeof(system_information_string), "%s_%s_%s", client_name, client_version, client_build_id);
+  snprintf(version_string, sizeof(version_string), "%s-%s", client_name, client_version);
+
   system_info.cpu_family = CPU_FAMILY__CPU_UNKNOWN;
   system_info.os = OS__OS_UNKNOWN;
-  snprintf(system_information_string, sizeof(system_information_string), "%s_%s_%s",
-    sp_sysinfo.client_name, sp_sysinfo.client_version, sp_sysinfo.client_build_id);
   system_info.system_information_string = system_information_string;
   system_info.device_id = sp_sysinfo.device_id;
-
+  system_info_from_uname(&system_info); // Sets cpu_family and os to actual values
-  system_info_from_uname(&system_info);
 
   client_response.login_credentials = &login_credentials;
   client_response.system_info = &system_info;
-  snprintf(version_string, sizeof(version_string), "%s-%s", sp_sysinfo.client_name, sp_sysinfo.client_version);
   client_response.version_string = version_string;
 
   len = client_response_encrypted__get_packed_size(&client_response);

src/inputs/librespot-c/tests/test1.c

@@ -258,9 +258,7 @@ main(int argc, char * argv[])
       goto error;
     }
 
-  snprintf(sysinfo.client_name, sizeof(sysinfo.client_name), "myclient");
+  memset(&sysinfo, 0, sizeof(struct sp_sysinfo));
-  snprintf(sysinfo.client_version, sizeof(sysinfo.client_version), "0.1");
-  snprintf(sysinfo.client_build_id, sizeof(sysinfo.client_build_id), "a");
   snprintf(sysinfo.device_id, sizeof(sysinfo.device_id), "aabbccddeeff");
 
   ret = librespotc_init(&sysinfo, &callbacks);

src/inputs/spotify_librespotc.c

@@ -304,7 +304,7 @@ struct sp_callbacks callbacks = {
 static int
 initialize(struct global_ctx *ctx)
 {
-  struct sp_sysinfo sysinfo;
+  struct sp_sysinfo sysinfo = { 0 };
   cfg_t *spotify_cfg;
   int ret;
 
@@ -316,9 +316,6 @@ initialize(struct global_ctx *ctx)
   if (ctx->is_initialized)
     return 0;
 
-  snprintf(sysinfo.client_name, sizeof(sysinfo.client_name), PACKAGE_NAME);
-  snprintf(sysinfo.client_version, sizeof(sysinfo.client_version), PACKAGE_VERSION);
-  snprintf(sysinfo.client_build_id, sizeof(sysinfo.client_build_id), "0");
   snprintf(sysinfo.device_id, sizeof(sysinfo.device_id), "%" PRIx64, libhash); // TODO use a UUID instead
 
   ret = librespotc_init(&sysinfo, &callbacks);