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imran-siddique merged 3 commits into from
Aug 27, 2026
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docs: settle MAX_REQUEST_BYTES provenance (#573) #585

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docs: record the 1MB proxy request cap
Yatsuiii Aug 27, 2026
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Merge branch 'main' into docs/573-request-cap
imran-siddique Aug 27, 2026
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Merge branch 'main' into docs/573-request-cap
imran-siddique Aug 27, 2026
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14 changes: 8 additions & 6 deletions docs/spec/proxy-security.md
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Expand Up @@ -2,7 +2,7 @@

---
Status: Draft v0.1
Last updated: 2026-06-04
Last updated: 2026-08-27
Stability: Unstable , expect breaking changes before v1.0
---

Expand Down Expand Up @@ -35,7 +35,7 @@ All items must be satisfied before Phase 2 ships. Items are non-negotiable; a pa
These constants are hard-coded in the proxy implementation. They are not configurable at runtime or via operator-supplied configuration. Making them configurable would allow an operator to raise limits and defeat the protection.

```python
MAX_REQUEST_BYTES = 10 * 1024 * 1024 # 10MB
MAX_REQUEST_BYTES = 1_000_000 # 1MB, decimal
MAX_JSON_NESTING_DEPTH = 64
MAX_PARSE_TIME_MS = 100
MAX_STRING_LENGTH = MAX_REQUEST_BYTES // 2 # per string field, see invariant below
Expand All @@ -49,13 +49,15 @@ The invariant matters because violating it produces a check that reads like a co

An implementation MUST derive the per-string cap from whatever whole-body cap it enforces. It MUST NOT restate the value as a literal, since a later change to the body cap then silently recreates the unreachable condition at a new ratio.

### Open: MAX_REQUEST_BYTES disagrees with the implementation
### MAX_REQUEST_BYTES is 1MB by design

This document states 10MB. Both implementations enforce 1MB: `scripts/mock_upstream.py` and `MCPServer.__init__` in `src/cmcp_runtime/mcp/server.py`.
Both implementations enforce `1_000_000`, decimal: `scripts/mock_upstream.py` and `MCPServer.__init__` in `src/cmcp_runtime/mcp/server.py`. This is the DOS-001 control created by [issue #147](https://github.com/agentrust-io/cmcp/issues/147), which established the request body limit before the gateway reads the body.

At the implemented 1MB, the per-string cap this document originally stated as a literal 1MB was exactly the whole-body cap, which is how the unreachable case above was found. Deriving the cap removes the dead-code hazard at either value, but the disagreement itself is still open: nothing records whether 1MB was a deliberate tightening or drift from this spec.
The per-string cap is therefore derived as `MAX_REQUEST_BYTES // 2`, which is 500,000 bytes at the current limit. Deriving it keeps the ratio explicit and prevents the per-string control from drifting when the body limit changes.

Tracked on #573. Implementers should follow the enforced body cap and the ratio above until that is settled, rather than raising a body cap to match this document.
`MAX_JSON_NESTING_DEPTH` and `MAX_PARSE_TIME_MS` must be implemented and evaluated against the 1MB request cap. Raising the cap to 10MB would be a separate resource and denial of service design decision, not a documentation correction.

The decision and its provenance are recorded in [issue #573](https://github.com/agentrust-io/cmcp/issues/573) and [DOS-001 issue #147](https://github.com/agentrust-io/cmcp/issues/147).

## Malformed Input Handling

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