A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911

Closed
#914
Closed
A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
#914
Assignees
nic-6443

Description

@janiussyafiq
janiussyafiq
opened on Aug 7, 2026

An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:

{"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.

The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:

  • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
  • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
  • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.

The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.

Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.

The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.

Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.

Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.

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    Skip to content
    A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911
    Closed
    #914
    Closed
    A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
    #914
    Assignees
    nic-6443
    Description
    @janiussyafiq
    janiussyafiq
    opened on Aug 7, 2026
    An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:
    {"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

    The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.
    The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:
    • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
    • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
    • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.
    The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.
    Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.
    The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.
    Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.
    Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.
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      Skip to content
      A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911
      Closed
      #914
      Closed
      A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
      #914
      Assignees
      nic-6443
      Description
      @janiussyafiq
      janiussyafiq
      opened on Aug 7, 2026
      An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:
      {"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

      The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.
      The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:
      • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
      • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
      • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.
      The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.
      Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.
      The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.
      Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.
      Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.
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        Skip to content
        A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911
        Closed
        #914
        Closed
        A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
        #914
        Assignees
        nic-6443
        Description
        @janiussyafiq
        janiussyafiq
        opened on Aug 7, 2026
        An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:
        {"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

        The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.
        The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:
        • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
        • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
        • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.
        The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.
        Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.
        The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.
        Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.
        Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.
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          Skip to content
          A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911
          Closed
          #914
          Closed
          A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
          #914
          Assignees
          nic-6443
          Description
          @janiussyafiq
          janiussyafiq
          opened on Aug 7, 2026
          An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:
          {"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

          The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.
          The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:
          • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
          • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
          • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.
          The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.
          Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.
          The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.
          Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.
          Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.
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var __m = "*";
var __re = new RegExp('^' + ".*" + '

            Skip to content
            A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911
            Closed
            #914
            Closed
            A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
            #914
            Assignees
            nic-6443
            Description
            @janiussyafiq
            janiussyafiq
            opened on Aug 7, 2026
            An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:
            {"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

            The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.
            The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:
            • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
            • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
            • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.
            The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.
            Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.
            The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.
            Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.
            Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.
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              Skip to content
              A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911
              Closed
              #914
              Closed
              A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
              #914
              Assignees
              nic-6443
              Description
              @janiussyafiq
              janiussyafiq
              opened on Aug 7, 2026
              An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:
              {"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

              The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.
              The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:
              • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
              • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
              • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.
              The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.
              Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.
              The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.
              Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.
              Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.
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                Skip to content
                A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call #911
                Closed
                #914
                Closed
                A2A: gateway never sends the A2A-Version header, so 1.0-pinned agents reject every call#911
                #914
                Assignees
                nic-6443
                Description
                @janiussyafiq
                janiussyafiq
                opened on Aug 7, 2026
                An A2A agent registered with protocol_version: "1.0" is unreachable through /a2a/<agent>, every call comes back with:
                {"error":{"code":-32009,"data":[{"@type":"type.googleapis.com/google.rpc.ErrorInfo",
"domain":"a2a-protocol.org","metadata":{},"reason":"VERSION_NOT_SUPPORTED"}],
"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'."}}

                The identical request sent straight to the agent with A2A-Version: 1.0 succeeds, and adding or omitting that header on the gateway call makes no difference.
                The gateway is the A2A client toward the upstream, and it never sends the A2A-Version header:
                • crates/aisix-proxy/src/a2a.rs:139 drops the inbound request parts (let (_parts, body) = request.into_parts();), so a caller-supplied A2A-Version never survives.
                • HttpBridge::send and fetch_agent_card in crates/aisix-a2a/src/bridge.rs set only Content-Type and the gateway-held credential.
                • A2aAgent.protocol_version is stored, validated and surfaced through the Admin API, but nothing in the data plane reads it. git log -S "A2A-Version" --all comes back empty — the header has never been sent, going back to the A2A DP MVP (feat(a2a): A2A (Agent-to-Agent) gateway — DP MVP #717) that introduced the field.
                The spec requires a client to send A2A-Version on every request, and requires an agent to interpret an absent value as 0.3 and answer VersionNotSupportedError when that version isn't supported. So the upstream silently downgrades to 0.3 and correctly rejects a 1.0-shaped body. The agent is behaving properly here; the gateway isn't. In practice this means protocol_version is non-functional and no A2A 1.0 agent can be reached through the gateway.
                Reproduced on main (2d7132e) against a stub agent that mirrors a2a-python 1.x negotiation: registering it with protocol_version: "1.0" reproduces the error above verbatim, and the stub logs no A2A-Version header on the inbound request from the gateway.
                The fix should be to carry protocol_version onto A2aUpstream and send it as A2A-Version on both send and fetch_agent_card. Tried locally: 1.0 agents then work whether or not the caller supplies the header, pinning 0.3 sends 0.3, and the aisix-a2a tests still pass.
                Worth deciding during implementation: whether a caller-supplied A2A-Version that disagrees with the registered protocol_version should be rejected, or just overridden by the pinned value.
                Separately, noticed while reproducing this, a2a_agent_card rewrites only the top-level url (crates/aisix-proxy/src/a2a.rs:258-260) and leaves supportedInterfaces[].url pointing at the upstream. A 1.0 client selects its endpoint from supportedInterfaces, so it would bypass the gateway entirely (losing auth, quota and usage tracking) and the internal upstream address leaks to callers. Can file that separately if it's out of scope here.
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