chasquid: Split Server and Conn

This patch moves chasquid's Server and Conn structures to their own
smtpsrv package, to make chasquid.go a bit more readable. It also helps
clarify the relation between Server and Conn.

There are no functional changes.

Note that git can still track the history across this commit (e.g. git
gui blame shows the right data).

internal/smtpsrv/conn_test.go

@@ -0,0 +1,60 @@
+package smtpsrv
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"blitiri.com.ar/go/chasquid/internal/domaininfo"
+	"blitiri.com.ar/go/chasquid/internal/spf"
+	"blitiri.com.ar/go/chasquid/internal/trace"
+)
+
+func TestSecLevel(t *testing.T) {
+	// We can't simulate this externally because of the SPF record
+	// requirement, so do a narrow test on Conn.secLevelCheck.
+	tmpDir, err := ioutil.TempDir("", "chasquid_test:")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	dinfo, err := domaininfo.New(tmpDir)
+	if err != nil {
+		t.Fatalf("Failed to create domain info: %v", err)
+	}
+
+	c := &Conn{
+		tr:    trace.New("testconn", "testconn"),
+		dinfo: dinfo,
+	}
+
+	// No SPF, skip security checks.
+	c.spfResult = spf.None
+	c.onTLS = true
+	if !c.secLevelCheck("from@slc") {
+		t.Fatalf("TLS seclevel failed")
+	}
+
+	c.onTLS = false
+	if !c.secLevelCheck("from@slc") {
+		t.Fatalf("plain seclevel failed, even though SPF does not exist")
+	}
+
+	// Now the real checks, once SPF passes.
+	c.spfResult = spf.Pass
+
+	if !c.secLevelCheck("from@slc") {
+		t.Fatalf("plain seclevel failed")
+	}
+
+	c.onTLS = true
+	if !c.secLevelCheck("from@slc") {
+		t.Fatalf("TLS seclevel failed")
+	}
+
+	c.onTLS = false
+	if c.secLevelCheck("from@slc") {
+		t.Fatalf("plain seclevel worked, downgrade was allowed")
+	}
+}