Simple non-proxying handler module for Nginx. Reads a set of headers and computes a checksum from these to build an ID-hash.
Compile Nginx with VisitorHash:
git submodule init
git submodule update
make
Simple test:
make run_local
curl 127.0.0.1:8080/hash --user-agent client3
outputs
Headers used for hash:
host: "127.0.0.1:8080"
user_agent: "client3"
user: ""
x_forwarded_for: "unknown value"
Hash becomes -377004896
The interesting function is ngx_http_hash_visitor_calc that reads the headers of interest and hashes them. I wrote a macro to minimize retyping of code for each header-variable.
The final body-string is ngx_snprintf'ed into a buffer. The buffer is dynamically-allocated in the handler-function using the nginx-pool. Only this buffer is heap-allocated which should keep things lean.
In a less performance-oriented environment, a loop and/or hash-table of headers with an iterative construction of the body-string may be more idiomatic. But here the body-string is constructed in one go.
Most of the rest of the c-file comes from the "empty gif" module:.