Handle pre-protocol errors to prevent memory exhaustion #1249
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When PostgreSQL cannot fork a backend process (e.g., an external process limit), it sends a plain text error like "Ecould not fork new process for connection: Resource temporarily unavailable" before any protocol handshake. The 'E' byte gets parsed as an ErrorResponse message type, but the following bytes are plain text, not a binary length field. This causes lib/pq to interpret ASCII text as a message length (e.g., "coul" = 0x636f756c = 1.6GB), leading to massive memory allocations and a likely OOM under connection pressure. This fix matches libpq's behavior in fe-connect.c: if an ErrorResponse has msgLength < 8 or > 30000, treat it as a pre-protocol plain text error and read it as a null-terminated string instead. There's a decent chance this is related to #638.
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When PostgreSQL cannot fork a backend process (e.g., an external process limit), it sends a plain text error like "Ecould not fork new process for connection: Resource temporarily unavailable" before any protocol handshake. The 'E' byte gets parsed as an ErrorResponse message type, but the following bytes are plain text, not a binary length field.
This causes lib/pq to interpret ASCII text as a message length (e.g., "coul" = 0x636f756c = 1.6GB), leading to massive memory allocations and a likely OOM under connection pressure.
This fix matches libpq's behavior in fe-connect.c: if an ErrorResponse has msgLength < 8 or > 30000, treat it as a pre-protocol plain text error and read it as a null-terminated string instead.
There's a decent chance this is related to #638.
Closes #1248