Improve NpgsqlCodec whitespace and quotation rules

pgLabII.PgUtils.Tests/ConnectionStrings/NpgsqlCodecTests.cs

@@ -46,7 +46,7 @@ public class NpgsqlCodecTests
         {
             Hosts = new [] { new HostEndpoint{ Host = "db.example.com", Port = 5432 } },
             Database = "prod db",
-            Username = "bob",
+            Username = "bob ",
             Password = "p;ss\"word",
             SslMode = SslMode.VerifyFull,
             ApplicationName = "cli app",
@@ -58,11 +58,12 @@ public class NpgsqlCodecTests
         var s = res.Value;
         Assert.Contains("Host=db.example.com", s);
         Assert.Contains("Port=5432", s);
-        Assert.Contains("Database=\"prod db\"", s);
-        Assert.Contains("Username=bob", s);
-        Assert.Contains("Password=\"p;ss\"\"word\"", s);
+        Assert.Contains("Database=prod db", s);
+        Assert.Contains("Username='bob '", s);
+        // Contains double-quote, no single-quote -> prefer single-quoted per DbConnectionStringBuilder-like behavior
+        Assert.Contains("Password='p;ss" + '"' + "word'", s);
         Assert.Contains("SSL Mode=VerifyFull", s);
-        Assert.Contains("Application Name=\"cli app\"", s);
+        Assert.Contains("Application Name=cli app", s);
         Assert.Contains("Timeout=9", s);
         Assert.Contains("Search Path=public", s);
     }
@@ -77,11 +78,12 @@ public class NpgsqlCodecTests
         var formatted = codec.TryFormat(parsed.Value);
         Assert.True(formatted.IsSuccess);
         var s = formatted.Value;
-        Assert.Contains("Host=\"my host\"", s);
+        Assert.Contains("Host=my host", s);
         Assert.Contains("Database=postgres", s);
         Assert.Contains("Username=me", s);
-        Assert.Contains("Password=\"with;quote\"\"\"", s);
-        Assert.Contains("Application Name=\"my app\"", s);
+        // Contains double-quote, no single-quote -> prefer single-quoted per DbConnectionStringBuilder-like behavior; parsed value contains one double-quote
+        Assert.Contains("Password='with;quote" + '"' + "'", s);
+        Assert.Contains("Application Name=my app", s);
         Assert.Contains("SSL Mode=Prefer", s);
     }
 }

pgLabII.PgUtils/ConnectionStrings/NpgsqlCodec.cs

@@ -236,24 +236,44 @@ public sealed class NpgsqlCodec : IConnectionStringCodec
     private static string FormatPair(string key, string? value)
     {
         value ??= string.Empty;
-        var needsQuotes = NeedsQuoting(value);
-        if (!needsQuotes) return key + "=" + value;
-        return key + "=\"" + EscapeQuoted(value) + "\"";
+        // Decide if we need quoting following DbConnectionStringBuilder rules:
+        // - Empty => quote
+        // - Leading or trailing whitespace => quote
+        // - Contains ';' or '=' => quote
+        // - Otherwise, no quotes, even if it contains internal whitespace
+        if (!NeedsQuoting(value))
+            return key + "=" + value;
+
+        // Choose single or double quotes. Prefer the one not present in the value; if both present, pick double and escape.
+        bool hasSingle = value.Contains('\'');
+        bool hasDouble = value.Contains('"');
+        if (!hasSingle)
+        {
+            // Use single quotes, escape single quotes by doubling when needed (not needed here since !hasSingle)
+            return key + "='" + value.Replace("'", "''") + "'";
+        }
+        if (!hasDouble)
+        {
+            // Use double quotes
+            return key + "=\"" + value.Replace("\"", "\"\"") + "\"";
+        }
+        // Value contains both quote types: default to double quotes and escape doubles by doubling
+        return key + "=\"" + value.Replace("\"", "\"\"") + "\"";
     }
 
     private static bool NeedsQuoting(string value)
     {
         if (value.Length == 0) return true;
-        foreach (var c in value)
-        {
-            if (char.IsWhiteSpace(c) || c == ';' || c == '=' || c == '"') return true;
-        }
+        // Leading or trailing whitespace requires quoting
+        if (char.IsWhiteSpace(value[0]) || char.IsWhiteSpace(value[^1])) return true;
+        // Special characters
+        if (value.IndexOf(';') >= 0 || value.IndexOf('=') >= 0) return true;
         return false;
     }
 
     private static string EscapeQuoted(string value)
     {
-        // Double the quotes per standard DbConnectionString rules
+        // Retained for compatibility, but not used directly; prefer inlined replacements in FormatPair
         return value.Replace("\"", "\"\"");
     }
 
@@ -279,19 +299,19 @@ public sealed class NpgsqlCodec : IConnectionStringCodec
 
             // read value
             string value;
-            if (i < input.Length && input[i] == '"')
+            if (i < input.Length && (input[i] == '"' || input[i] == '\''))
             {
-                i++; // skip opening quote
+                char quote = input[i++]; // opening quote (' or ")
                 var sb = new StringBuilder();
                 while (i < input.Length)
                 {
                     char c = input[i++];
-                    if (c == '"')
+                    if (c == quote)
                     {
-                        if (i < input.Length && input[i] == '"')
+                        if (i < input.Length && input[i] == quote)
                         {
                             // doubled quote -> literal quote
-                            sb.Append('"');
+                            sb.Append(quote);
                             i++;
                             continue;
                         }
@@ -311,6 +331,7 @@ public sealed class NpgsqlCodec : IConnectionStringCodec
             {
                 int valStart = i;
                 while (i < input.Length && input[i] != ';') i++;
+                // Unquoted value: per DbConnectionStringBuilder, leading/trailing whitespace is ignored
                 value = input.Substring(valStart, i - valStart).Trim();
             }