add builder interface for making servers (#1122)

.github/workflows/rust.yml

@@ -11,6 +11,7 @@ on:
 
 env:
   CARGO_TERM_COLOR: always
+  RUST_BACKTRACE: 1
 
 jobs:
   check-style:

CHANGELOG.adoc

@@ -15,6 +15,54 @@
 
 https://github.com/oxidecomputer/dropshot/compare/v0.12.0\...HEAD[Full list of commits]
 
+* https://github.com/oxidecomputer/dropshot/pull/1122[#1122] Adds a new `ServerBuilder` as the primary way of constructing a Dropshot server.  This replaces `HttpServerStarter::new()` and `HttpServerStarter::new_with_tls()`.  These older functions still exist for compatibility.  They may be removed in an upcoming release, along with the `HttpServerStarter`.
++
+In this release, using the builder interface is not very different from using these older functions.  But as we look at adding new construction-time options (e.g., for API versioning), those will only be added to the builder.
++
+The builder also provides structured errors rather than the `GenericError` provided by these older functions.
++
+Most non-TLS callers were using `HttpServerStarter::new()` and then calling `start()` right away.  In that case, you can replace:
++
+```rust
+HttpServerStarter::new(&config, api, private, &log).map_err(...)?.start()
+```
++
+with:
++
+```rust
+ServerBuilder::new(api, private, log).config(config).start().map_err(...)?
+```
++
+If you were using `HttpServerStarter::new_with_tls()`, you'd similarly replace:
++
+```rust
+HttpServerStarter::new_with_tls(&config, api, private, &log, tls).map_err(...)?.start()
+```
++
+with:
++
+```rust
+ServerBuilder::new(api, private, log).config(config).tls(tls).start().map_err(...)?
+```
++
+If you were _not_ invoking `start()` immediately before, you can still construct an intermediate starter object with `build_starter()`.  If you were doing this:
++
+```rust
+let starter = HttpServerStarter::new(&config, api, private, &log).map_err(...)?;
+...
+starter.start()
+```
++
+Then you can now do:
++
+```rust
+let starter = ServerBuilder::new(api, private, log).config(config).build_starter().map_err(...)?;
+...
+starter.start()
+```
++
+We'd like to remove the `HttpServerStarter` altogether, so let us know if you're still using it for some reason.
+
 == 0.12.0 (released 2024-09-26)
 
 https://github.com/oxidecomputer/dropshot/compare/v0.11.0\...v0.12.0[Full list of commits]