[M5] mxaccess-asb: WCF binary message header (action+to dict pre-pop)

Adds the binary header block that WCF prepends to SizedEnvelope
payloads. Reverse-engineered from .NET probe wire bytes captured via
asb-relay.

Wire form (per the .NET capture analysis in the previous commit):
```
[outer length, multibyte-int31]
  [string-1 length, multibyte-int31] [UTF-8 bytes]   ← dict id 1 (action)
  [string-2 length, multibyte-int31] [UTF-8 bytes]   ← dict id 3 (to)
[NBFX <s:Envelope>...]
```

Inside the NBFX envelope, `<a:Action>` and `<a:To>` reference the
pre-pop strings via `DictionaryText 0xAA {odd-id}` instead of inlining
their values. The header strings get assigned odd dict ids
(1, 3, 5, ...); even ids stay reserved for the [MC-NBFS] static dict.

Encode side:
* `encode_envelope` now emits header [action, to] before NBFX. `to_uri`
  defaults to empty string when None — caller-supplied `with_to(uri)`
  is the supported path.
* AsbClient's `send_envelope` and `send_envelope_one_way` auto-fill
  `to_uri` from `self.via_uri` when not set.
* New private `encode_binary_header(strings)` helper.

Decode side:
* New `parse_binary_header_prefix(input)` heuristically detects + parses
  the header (look for plausible NBFX element record byte 0x40-0x77 at
  the offset implied by the outer length).
* New `resolve_with_header(text, dynamic, header)` resolves
  `DictionaryText` with odd id by indexing into header.strings; even
  ids fall through to static-dict lookup as before.

Tests pass (72) — round-trip envelope → bytes → envelope recovers
action through the new dict-id resolution path.

Live status: this commit gets us further but the connect SOAP
envelope still TCP-RSTs at SMSvcHost. The remaining delta vs the .NET
capture is structural NBFX optimisation: .NET uses single-letter
prefix-element/attribute records (0x44-0x77 PrefixDictionaryElement
_<a-z>, 0x0C-0x25 PrefixDictionaryAttribute_<a-z>, 0x0B
DictionaryXmlnsAttribute) while our F21 encoder always uses the long
forms (0x43 prefix-string + name-dict-id, etc.). Logically
equivalent but WCF's parser likely strict on which form it accepts.

Next iteration will add short-form encoding to F21 for single-letter
prefixes (s:, a:, h:, i:) which covers every namespace prefix in our
envelope.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

rust/crates/mxaccess-asb/src/client.rs

@@ -152,7 +152,16 @@ impl<T: AsyncRead + AsyncWrite + Unpin + Send> AsbClient<T> {
             return Err(ClientError::AlreadyClosed);
         }
 
-        let payload = encode_envelope(envelope, &mut self.write_dictionary)?;
+        // Default the WS-Addressing To header to the same URL we put
+        // in the NMF Via record. WCF dispatches by To-URL match
+        // against the registered service URL; an empty / wrong To
+        // produces an AddressFilterMismatch fault.
+        let envelope = if envelope.to_uri.is_some() {
+            envelope.clone()
+        } else {
+            envelope.clone().with_to(self.via_uri.clone())
+        };
+        let payload = encode_envelope(&envelope, &mut self.write_dictionary)?;
         let mut framed = Vec::new();
         NmfRecord::SizedEnvelope(payload).encode_into(&mut framed)?;
         self.stream.write_all(&framed).await?;
@@ -276,7 +285,12 @@ impl<T: AsyncRead + AsyncWrite + Unpin + Send> AsbClient<T> {
         if self.closed {
             return Err(ClientError::AlreadyClosed);
         }
-        let payload = encode_envelope(envelope, &mut self.write_dictionary)?;
+        let envelope = if envelope.to_uri.is_some() {
+            envelope.clone()
+        } else {
+            envelope.clone().with_to(self.via_uri.clone())
+        };
+        let payload = encode_envelope(&envelope, &mut self.write_dictionary)?;
         let mut framed = Vec::new();
         NmfRecord::SizedEnvelope(payload).encode_into(&mut framed)?;
         self.stream.write_all(&framed).await?;

rust/crates/mxaccess-asb/src/envelope.rs

@@ -169,108 +169,131 @@ impl SoapEnvelope {
 }
 
 /// Encode a SOAP envelope to NBFX bytes. Returns the byte buffer + the
-/// dynamic dictionary state at end-of-encode (the F25 client threads
+/// dynamic dictionary state at end-of-encode.
-/// that through subsequent envelopes for compression).
 ///
-/// Wire shape:
+/// **Wire shape (WCF binary message format)**:
-/// ```xml
+///
-/// <s:Envelope>                          (dict 4 / 2)
+/// 1. **Binary header block** prepended to the NBFX envelope. WCF
-///   <s:Header>                          (dict 8)
+///    uses this to pre-populate the per-session dynamic dictionary
-///     <a:Action s:mustUnderstand="1">…</a:Action>   (dict 10)
+///    with strings that appear inside the envelope. Each string gets
-///     [<h:ConnectionValidator …/>]      (asb headers ns)
+///    an odd dictionary id (`1, 3, 5, ...` — even ids are reserved
-///   </s:Header>
+///    for the static [MC-NBFS] dictionary).
-///   <s:Body>                            (dict 14)
+///
-///     {body_tokens}
+///    ```text
-///   </s:Body>
+///    [outer length, multibyte-int31]
-/// </s:Envelope>
+///      [action length, multibyte-int31] [action UTF-8 bytes]   ← dict id 1
-/// ```
+///      [to length,     multibyte-int31] [to UTF-8 bytes]       ← dict id 3
+///    ```
+///
+/// 2. **NBFX envelope** that references the pre-populated strings:
+///
+///    ```xml
+///    <s:Envelope xmlns:s="…" xmlns:a="…">
+///      <s:Header>
+///        <a:Action s:mustUnderstand="1">{dict 1}</a:Action>
+///        [<h:ConnectionValidator …/>]
+///        <a:MessageID>urn:uuid:…</a:MessageID>
+///        <a:ReplyTo><a:Address>{anonymous}</a:Address></a:ReplyTo>
+///        <a:To s:mustUnderstand="1">{dict 3}</a:To>
+///      </s:Header>
+///      <s:Body>{body_tokens}</s:Body>
+///    </s:Envelope>
+///    ```
+///
+/// The header form was reverse-engineered from the .NET reference's
+/// wire bytes (captured via `examples/asb-relay`); see `[M5]
+/// live-probe iteration` commits in the followups for the full
+/// derivation.
 pub fn encode_envelope(
     envelope: &SoapEnvelope,
     dynamic: &mut DynamicDictionary,
 ) -> Result<Vec<u8>, NbfxError> {
+    // ---- Binary header block ----
+    //
+    // Pre-populate the per-session dynamic dictionary with strings the
+    // NBFX envelope below references. Each string gets an odd dict id
+    // (`1, 3, 5, ...` — even ids are reserved for [MC-NBFS] static).
+    // We always include action + to even when `to_uri` is None: in
+    // that case we use an empty string for the To slot. WCF's default
+    // service dispatcher requires both populated for net.tcp.
+    let to_uri = envelope.to_uri.clone().unwrap_or_default();
+    let action_dict_id: u32 = 1;
+    let to_dict_id: u32 = 3;
+    let header_strings = [envelope.action.as_str(), to_uri.as_str()];
+
+    // ---- NBFX envelope tokens ----
     let mut tokens = vec![
-        // <s:Envelope xmlns:s="…soap-envelope" xmlns:a="…addressing">
         NbfxToken::Element {
             prefix: Some("s".to_string()),
             name: NbfxName::Static(ns::ENVELOPE),
         },
+        NbfxToken::NamespaceDeclaration {
+            prefix: "s".to_string(),
+            value: NbfxText::DictionaryStatic(ns::SOAP_ENVELOPE),
+        },
+        NbfxToken::NamespaceDeclaration {
+            prefix: "a".to_string(),
+            value: NbfxText::DictionaryStatic(ns::WS_ADDRESSING),
+        },
+        // <s:Header>
+        NbfxToken::Element {
+            prefix: Some("s".to_string()),
+            name: NbfxName::Static(ns::HEADER),
+        },
+        // <a:Action s:mustUnderstand="1">{dict id 1}</a:Action>
+        NbfxToken::Element {
+            prefix: Some("a".to_string()),
+            name: NbfxName::Static(ns::ACTION),
+        },
+        NbfxToken::Attribute {
+            prefix: Some("s".to_string()),
+            name: NbfxName::Static(ns::MUST_UNDERSTAND_ATTR),
+            value: NbfxText::One,
+        },
+        NbfxToken::Text(NbfxText::DictionaryStatic(action_dict_id)),
+        NbfxToken::EndElement, // </a:Action>
     ];
-    tokens.push(NbfxToken::NamespaceDeclaration {
-        prefix: "s".to_string(),
-        value: NbfxText::DictionaryStatic(ns::SOAP_ENVELOPE),
-    });
-    tokens.push(NbfxToken::NamespaceDeclaration {
-        prefix: "a".to_string(),
-        value: NbfxText::DictionaryStatic(ns::WS_ADDRESSING),
-    });
 
-    //   <s:Header>
+    //     <h:ConnectionValidator …/>  (when present, comes before
-    tokens.push(NbfxToken::Element {
+    //     MessageID/ReplyTo per the .NET dump's element order)
-        prefix: Some("s".to_string()),
+    if let Some(v) = &envelope.validator {
-        name: NbfxName::Static(ns::HEADER),
+        encode_validator(&mut tokens, v, dynamic);
-    });
+    }
 
-    //     <a:Action s:mustUnderstand="1">{action}</a:Action>
+    //     <a:MessageID>urn:uuid:{uuid}</a:MessageID>
+    let message_id = format!("urn:uuid:{}", make_random_uuid_v4());
     tokens.push(NbfxToken::Element {
         prefix: Some("a".to_string()),
-        name: NbfxName::Static(ns::ACTION),
+        name: NbfxName::Static(26),
+    });
+    tokens.push(NbfxToken::Text(NbfxText::Chars(message_id)));
+    tokens.push(NbfxToken::EndElement); // </a:MessageID>
+
+    //     <a:ReplyTo><a:Address>{anonymous}</a:Address></a:ReplyTo>
+    tokens.push(NbfxToken::Element {
+        prefix: Some("a".to_string()),
+        name: NbfxName::Static(44),
+    });
+    tokens.push(NbfxToken::Element {
+        prefix: Some("a".to_string()),
+        name: NbfxName::Static(42),
+    });
+    tokens.push(NbfxToken::Text(NbfxText::DictionaryStatic(20)));
+    tokens.push(NbfxToken::EndElement); // </a:Address>
+    tokens.push(NbfxToken::EndElement); // </a:ReplyTo>
+
+    //     <a:To s:mustUnderstand="1">{dict id 3}</a:To>
+    tokens.push(NbfxToken::Element {
+        prefix: Some("a".to_string()),
+        name: NbfxName::Static(12),
     });
     tokens.push(NbfxToken::Attribute {
         prefix: Some("s".to_string()),
         name: NbfxName::Static(ns::MUST_UNDERSTAND_ATTR),
         value: NbfxText::One,
     });
-    tokens.push(NbfxToken::Text(NbfxText::Chars(envelope.action.clone())));
+    tokens.push(NbfxToken::Text(NbfxText::DictionaryStatic(to_dict_id)));
-    tokens.push(NbfxToken::EndElement); // </a:Action>
+    tokens.push(NbfxToken::EndElement); // </a:To>
-
-    //     <h:ConnectionValidator …/>  (WCF dump shows this comes BEFORE
-    //     MessageID/ReplyTo when present)
-    if let Some(v) = &envelope.validator {
-        encode_validator(&mut tokens, v, dynamic);
-    }
-
-    //     <a:MessageID>urn:uuid:{uuid}</a:MessageID>
-    // WCF's default binding requires MessageID for two-way operations.
-    // We auto-generate one per envelope; the value is opaque to the
-    // service but must be a valid URI.
-    let message_id = format!("urn:uuid:{}", make_random_uuid_v4());
-    tokens.push(NbfxToken::Element {
-        prefix: Some("a".to_string()),
-        name: NbfxName::Static(26), // "MessageID"
-    });
-    tokens.push(NbfxToken::Text(NbfxText::Chars(message_id)));
-    tokens.push(NbfxToken::EndElement); // </a:MessageID>
-
-    //     <a:ReplyTo>
-    //       <a:Address>http://www.w3.org/2005/08/addressing/anonymous</a:Address>
-    //     </a:ReplyTo>
-    tokens.push(NbfxToken::Element {
-        prefix: Some("a".to_string()),
-        name: NbfxName::Static(44), // "ReplyTo"
-    });
-    tokens.push(NbfxToken::Element {
-        prefix: Some("a".to_string()),
-        name: NbfxName::Static(42), // "Address"
-    });
-    tokens.push(NbfxToken::Text(NbfxText::DictionaryStatic(20))); // anonymous
-    tokens.push(NbfxToken::EndElement); // </a:Address>
-    tokens.push(NbfxToken::EndElement); // </a:ReplyTo>
-
-    //     <a:To s:mustUnderstand="1">{to_uri}</a:To>  (optional — WCF
-    //     omits To for net.tcp request/response by default)
-    if let Some(to) = &envelope.to_uri {
-        tokens.push(NbfxToken::Element {
-            prefix: Some("a".to_string()),
-            name: NbfxName::Static(12), // "To"
-        });
-        tokens.push(NbfxToken::Attribute {
-            prefix: Some("s".to_string()),
-            name: NbfxName::Static(ns::MUST_UNDERSTAND_ATTR),
-            value: NbfxText::One,
-        });
-        tokens.push(NbfxToken::Text(NbfxText::Chars(to.clone())));
-        tokens.push(NbfxToken::EndElement);
-    }
 
     tokens.push(NbfxToken::EndElement); // </s:Header>
 
@@ -284,8 +307,121 @@ pub fn encode_envelope(
 
     tokens.push(NbfxToken::EndElement); // </s:Envelope>
 
-    let mut out = Vec::with_capacity(estimate_envelope_size(envelope));
+    // ---- Assemble output: binary header + NBFX envelope ----
-    encode_tokens(&tokens, dynamic, &mut out)?;
+    let mut nbfx_bytes = Vec::with_capacity(estimate_envelope_size(envelope));
+    encode_tokens(&tokens, dynamic, &mut nbfx_bytes)?;
+
+    let header_bytes = encode_binary_header(&header_strings)?;
+
+    let mut out = Vec::with_capacity(header_bytes.len() + nbfx_bytes.len());
+    out.extend_from_slice(&header_bytes);
+    out.extend_from_slice(&nbfx_bytes);
+    Ok(out)
+}
+
+/// Encode the WCF binary message header that prepends the NBFX envelope.
+/// The header pre-populates the per-session dynamic dictionary with
+/// `strings`, in order — the first gets dict id 1, the second id 3,
+/// etc. (odd ids only; evens are reserved for static `[MC-NBFS]`).
+///
+/// Wire format:
+/// ```text
+/// [outer length as multibyte-int31]
+///   [string 1 length as multibyte-int31] [UTF-8 bytes]
+///   [string 2 length as multibyte-int31] [UTF-8 bytes]
+///   ...
+/// ```
+/// Parsed WCF binary header: the strings pre-populated into the
+/// session dynamic dictionary + the byte offset where the NBFX
+/// envelope begins.
+struct ParsedBinaryHeader {
+    /// Pre-pop strings in declaration order. Wire ids: index 0 → 1,
+    /// index 1 → 3, index 2 → 5, etc. (odd numbers; even reserved
+    /// for `[MC-NBFS]` static dict).
+    strings: Vec<String>,
+    nbfx_start: usize,
+}
+
+/// Detect + decode the WCF binary header block at the start of a SOAP
+/// envelope payload. Returns `None` if no header is present (e.g. the
+/// peer didn't emit one).
+///
+/// Heuristic: read a multibyte-int31 length L from the start. If the
+/// byte at offset 1+L is a plausible NBFX element record byte
+/// (`0x40`-`0x77`), treat the first 1+L bytes as the header. Walk the
+/// inner block as a sequence of length-prefixed UTF-8 strings.
+fn parse_binary_header_prefix(input: &[u8]) -> Option<ParsedBinaryHeader> {
+    use mxaccess_asb_nettcp::nmf::decode_multibyte_int31;
+    let mut cursor = 0usize;
+    let outer_len = decode_multibyte_int31(input, &mut cursor).ok()?;
+    let outer_len = usize::try_from(outer_len).ok()?;
+    let header_start = cursor;
+    let nbfx_start = header_start + outer_len;
+    if nbfx_start >= input.len() {
+        return None;
+    }
+    let first_nbfx = *input.get(nbfx_start)?;
+    if !(0x40..=0x77).contains(&first_nbfx) {
+        return None;
+    }
+    // Walk the inner block as (multibyte-int31 length, UTF-8 bytes).
+    let mut strings = Vec::new();
+    let mut p = header_start;
+    let header_end = header_start + outer_len;
+    while p < header_end {
+        let str_len = decode_multibyte_int31(input, &mut p).ok()?;
+        let str_len = usize::try_from(str_len).ok()?;
+        let bytes = input.get(p..p + str_len)?;
+        let s = std::str::from_utf8(bytes).ok()?;
+        strings.push(s.to_string());
+        p += str_len;
+    }
+    Some(ParsedBinaryHeader {
+        strings,
+        nbfx_start,
+    })
+}
+
+/// Resolve an NBFX text token using static dict + dynamic dict + the
+/// binary-header pre-pop strings (odd dict ids).
+fn resolve_with_header(
+    text: &NbfxText,
+    dynamic: &DynamicDictionary,
+    header: Option<&ParsedBinaryHeader>,
+) -> Option<String> {
+    if let NbfxText::DictionaryStatic(id) = text {
+        // Even ids hit the static dict; odd ids hit the dynamic
+        // pre-pop. Wire id 2N+1 → header.strings[N].
+        if id % 2 == 1 {
+            if let Some(h) = header {
+                let idx = (*id as usize - 1) / 2;
+                if let Some(s) = h.strings.get(idx) {
+                    return Some(s.clone());
+                }
+            }
+        }
+    }
+    text.resolve(dynamic)
+}
+
+fn encode_binary_header(strings: &[&str]) -> Result<Vec<u8>, NbfxError> {
+    use mxaccess_asb_nettcp::nmf::encode_multibyte_int31;
+    let mut inner = Vec::new();
+    for s in strings {
+        let len = i32::try_from(s.len()).map_err(|_| NbfxError::PayloadTooLarge {
+            len: s.len(),
+            max: i32::MAX as u64,
+        })?;
+        encode_multibyte_int31(&mut inner, len).map_err(|_| NbfxError::IntOverflow)?;
+        inner.extend_from_slice(s.as_bytes());
+    }
+    let inner_len = i32::try_from(inner.len()).map_err(|_| NbfxError::PayloadTooLarge {
+        len: inner.len(),
+        max: i32::MAX as u64,
+    })?;
+    let mut out = Vec::new();
+    encode_multibyte_int31(&mut out, inner_len).map_err(|_| NbfxError::IntOverflow)?;
+    out.extend_from_slice(&inner);
     Ok(out)
 }
 
@@ -306,7 +442,31 @@ pub fn decode_envelope(
     input: &[u8],
     dynamic: &mut DynamicDictionary,
 ) -> Result<DecodedEnvelope, EnvelopeError> {
-    let (tokens, _consumed) = decode_tokens(input, dynamic)?;
+    // Strip + decode the WCF binary header block (action+to pre-pop)
+    // if present. The header strings get assigned odd dict ids
+    // (1, 3, 5, ...); inside the NBFX envelope they're referenced via
+    // `DictionaryText (0xAA) {odd-id}`. We feed each into the F21
+    // dynamic dictionary at the matching offset so `text.resolve()`
+    // returns the right string.
+    let header = parse_binary_header_prefix(input);
+    let nbfx_input = match &header {
+        Some(h) => input.get(h.nbfx_start..).unwrap_or(input),
+        None => input,
+    };
+    if let Some(h) = &header {
+        // F21's DynamicDictionary uses sequential ids starting at 0.
+        // Wire ids for dynamic strings are odd (1, 3, 5, ...).
+        // Prefill our internal dict with sentinel placeholders at
+        // even indices so the strings land at odd ones via `intern`.
+        for (i, s) in h.strings.iter().enumerate() {
+            // Slot 0 → wire id 1, slot 1 → wire id 3, etc. Since
+            // intern just appends, this works as long as we intern
+            // header strings before any other dynamic-dict use.
+            let _ = i; // silence unused-var if we change scheme later
+            dynamic.intern(s);
+        }
+    }
+    let (tokens, _consumed) = decode_tokens(nbfx_input, dynamic)?;
     let mut action = None;
     let mut validator: Option<ConnectionValidator> = None;
     let mut body_tokens = Vec::new();
@@ -320,7 +480,7 @@ pub fn decode_envelope(
             } if *id == ns::ACTION => {
                 idx = consume_attributes(&tokens, idx + 1);
                 if let Some(NbfxToken::Text(text)) = tokens.get(idx) {
-                    action = text.resolve(dynamic);
+                    action = resolve_with_header(text, dynamic, header.as_ref());
                     idx += 1;
                 }
                 idx = skip_until_end(&tokens, idx);

rust/crates/mxaccess/examples/asb-preamble-probe.rs

@@ -48,8 +48,9 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let connection_id = [0xAAu8; 16];
     let public_key = vec![0xBBu8; 32];
     let body = build_connect_request_body(connection_id, &public_key);
-    let envelope = SoapEnvelope::new(actions::CONNECT).with_body_tokens(body);
+    let envelope = SoapEnvelope::new(actions::CONNECT)
-    let _ = via.clone(); // keep $via in scope for the eprintln above
+        .with_to(&via)
+        .with_body_tokens(body);
     let mut dynamic = DynamicDictionary::new();
     let payload = encode_envelope(&envelope, &mut dynamic)?;
     eprintln!("envelope NBFX bytes: {}", payload.len());

rust/crates/mxaccess/examples/asb-relay.rs

@@ -43,8 +43,8 @@
 //! connects to us, but the URL inside the preamble routes correctly
 //! at SMSvcHost).
 
-use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
 
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::{TcpListener, TcpStream};