envoyproxy/envoy

ext_proc: xds.virtual_host_metadata unparseable due to DebugString serialization (Envoy 1.37.0)

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#43466 opened on Feb 12, 2026

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Description

Title: Virtual host metadata uses DebugString instead of TextFormat (Protobuf 30+ incompatible)

Description:

Envoy 1.37.0 serializes the xds.virtual_host_metadata attribute using DebugString() instead of TextFormat::PrintToString(). With Protobuf 30+, this produces unparseable output prefixed with goo.gle/debugonly or goo.gle/debugstr.

External processor (ext_proc) implementations cannot parse the virtual host metadata because Protobuf 30+ intentionally adds these prefixes to prevent parsing (see https://protobuf.dev/programming-guides/deserialize-debug/).

Expected behavior: Metadata should be serialized using TextFormat::PrintToString() to produce machine-readable protobuf text format that can be parsed by standard protobuf libraries.

Repro steps:

  1. Deploy Envoy 1.37.0 with an external processor configuration
  2. Configure virtual host metadata.
  3. External processor receives xds.virtual_host_metadata attribute in ProcessingRequest
  4. Attempt to parse the string value as protobuf text format
  5. Parsing fails with: proto: syntax error (line 1:1): invalid field name: goo.gle/debugonly

Environment: Envoy 1.37.0

Logs:

Sample metadata received by ext_proc:

goo.gle/debugonly  filter_metadata { key: "someKey" value { fields { key: "apiIdentifier" value { string_value: "..." } } fields { key: "extHost" value { string_value: "..." } } } }

Error when parsing:

proto: syntax error (line 1:1): invalid field name: goo.gle/debugonly

Impact:

Breaking change from 1.36 to 1.37 - makes virtual host metadata unparseable by ext_proc implementations using standard protobuf libraries (Go, Python, Java, C++).

Contributor guide

Tech stack
cppgrpc
Domain
backendinfrastructureobservability
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
C++ knowledgeProtobuf basicsEnvoy ext proc filter
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Locate the ext proc filter code in source/extensions/filters/http/ext proc/ that serializes virtual host metadata. Replace calls to DebugString() with TextFormat::PrintToString() to produce parseable protobuf text format. Ensure compatibility with older Protobuf versions. Check for any other uses of DebugString that might also need updating. The change is localized and well defined, but requires understanding of protobuf serialization and Envoy's build system.