fix: preserve original JSON bytes in normalizeCacheControlTTL#407
fix: preserve original JSON bytes in normalizeCacheControlTTL#407thebtf wants to merge 1 commit intorouter-for-me:mainfrom
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… TTL change needed normalizeCacheControlTTL unconditionally re-serializes the entire request body through json.Unmarshal/json.Marshal even when no TTL normalization is needed. Go's json.Marshal randomizes map key order and HTML-escapes <, >, & characters (to \u003c, \u003e, \u0026), producing different raw bytes on every call. Anthropic's prompt caching uses byte-prefix matching, so any byte-level difference causes a cache miss. This means the ~119K system prompt and tools are re-processed on every request when routed through CPA. The fix adds a bool return to normalizeTTLForBlock to indicate whether it actually modified anything, and skips the marshal step in normalizeCacheControlTTL when no blocks were changed.
Summary of ChangesHello, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request optimizes the Highlights
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Code Review
This pull request correctly addresses an issue where normalizeCacheControlTTL would always re-serialize the JSON payload, causing unnecessary cache misses due to byte-level differences. The change to return the original byte slice when no modifications are made is a solid improvement for performance and correctness. The addition of a new test case to verify this behavior is also great. I have one suggestion to improve code maintainability by reducing some duplication.
| if tools, ok := asArray(root["tools"]); ok { | ||
| for _, tool := range tools { | ||
| if obj, ok := asObject(tool); ok { | ||
| normalizeTTLForBlock(obj, &seen5m) | ||
| if normalizeTTLForBlock(obj, &seen5m) { | ||
| modified = true | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| if system, ok := asArray(root["system"]); ok { | ||
| for _, item := range system { | ||
| if obj, ok := asObject(item); ok { | ||
| normalizeTTLForBlock(obj, &seen5m) | ||
| if normalizeTTLForBlock(obj, &seen5m) { | ||
| modified = true | ||
| } | ||
| } | ||
| } | ||
| } |
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The logic for iterating over tools and system arrays is identical. This pattern is also repeated for the content array within each message. To improve maintainability and reduce code duplication, consider extracting this iteration logic into a local helper function.
For example:
processItems := func(items []any) {
for _, item := range items {
if obj, ok := asObject(item); ok {
if normalizeTTLForBlock(obj, &seen5m) {
modified = true
}
}
}
}
if tools, ok := asArray(root["tools"]); ok {
processItems(tools)
}
// ... and so on for system and messages content1 participant
Summary
normalizeCacheControlTTLunconditionally re-serializes the entire request body throughjson.Unmarshal→json.Marshal, even when no TTL normalization is neededjson.Marshal(map[string]any)randomizes map key order and HTML-escapes<,>,&(→\u003c,\u003e,\u0026), producing different raw bytes on every callChanges
normalizeTTLForBlocknow returnsboolindicating whether it modified the blocknormalizeCacheControlTTLtracks amodifiedflag and returns the originalpayloadslice unchanged when no TTL downgrade was neededTestNormalizeCacheControlTTL_PreservesOriginalBytesWhenNoChangeverifies exact byte preservation (including HTML chars thatjson.Marshalwould escape)Test plan
go build ./...— clean buildgo test ./internal/runtime/executor/... -run TestNormalizeCacheControlTTL— both tests passgo test ./internal/runtime/executor/...— all existing tests unaffected