fix: HTTP formatting constraints (#78)

* fix: http headers max

* fix: verify HTTP machine state at end

circuits/http/machine.circom

@@ -90,8 +90,8 @@ template StateChange() {
     // enable parsing header on reading CRLF
     signal enableParsingHeader <== readCRLF * isParsingStart;
     // check if we are parsing header
-    // TODO: correct this 3 (it means we can parse max 2^3 headers)
-    signal isParsingHeader <== GreaterEqThan(3)([state[1], 1]);
+    // Allows for max headers to be 2^5 = 32
+    signal isParsingHeader <== GreaterEqThan(5)([state[1], 1]);
     // increment parsing header counter on CRLF and parsing header
     signal incrementParsingHeader <== readCRLF * isParsingHeader;
     // disable parsing header on reading CRLF-CRLF

circuits/http/verification.circom

@@ -78,4 +78,12 @@ template HTTPVerification(DATA_BYTES, MAX_NUMBER_OF_HEADERS) {
     body_hash_equal_check        === 1;
 
     step_out[0] <== inner_body_hash;
+
+    // Verify machine ends in a valid state
+    State[DATA_BYTES - 1].next_parsing_start       === 0;
+    State[DATA_BYTES - 1].next_parsing_header      === 0;
+    State[DATA_BYTES - 1].next_parsing_field_name  === 0;
+    State[DATA_BYTES - 1].next_parsing_field_value === 0;
+    State[DATA_BYTES - 1].next_parsing_body        === 1;
+    State[DATA_BYTES - 1].next_line_status         === 0;
 }