firebase-upstream-server is an implementation of the Firebase XMPP Connection Server protocol in C.

It connects to the FCM XMPP servers using a configuration file (--conf <file>), and sends line-delimited JSON to stdout. Informational, debug, and error messages are sent to stderr.

There are command line options available for alternative JSON-streaming formats:

• application/json-seq (--seq)
• length-prefixed (--len-prefixed)
• concatenated (--concat)
• NUL-terminated (--null, -Z)

It is currently minimally functional.

• Supports simultaneous connections to multiple servers using multiple accounts.
• Connection draining support using threading (untested).
• Automatic reconnection using exponential back-off (128 second maximum between retries).

From the src directory, run the following commands (other C compilers are available):

gcc -c config-parse.c
gcc -c firebase-upstream-server.c
gcc -o firebase-upstream-server firebase-upstream-server.o config-parse.o -lconfig -lssl -lcrypto -lstrophe -ljson-c -lpthread

firebase-upstream-server requires:

• libstrophe and its dependencies (libexpat/libxml2, openssl)
• openssl
• libconfig
• libjson-c

See conf/xmpp.conf.example for an example configuration file.