Perform magic checks on a database file for better error messaging.

.gitignore

@@ -1,10 +1,13 @@
 experiments/imdb/*
+!experiments/imdb/*.nim
+!experiments/imdb/Makefile
 nimble.paths
 config.nims
 tmp/*
 kuzu
 nimcache/*
 tests/*
+!tests/*/t_*.nim
 testresults/*
 testresults.html
 

USAGE.md

@@ -358,8 +358,10 @@ Manually rewind the `KuzuQueryResult` via `rewind()`.
 
 ## Multiple Query Results
 
-A query can potentially return any number of separate statements.  Iterate over
-linked `KuzuQueryResult` objects with the `sets()` iterator.
+A query can potentially return any number of separate statements.  In the case
+of more potential `RETURN`s, the query will only contain the first.  Iterate
+over linked `KuzuQueryResult` objects with the `sets()` iterator to retreive the
+remaining:
 
 ```nim
 import kuzu

kuzu.nimble

@@ -18,9 +18,7 @@ task makewrapper, "Generate the C wrapper using Futhark":
 task test, "Run the test suite.":
     exec "testament --megatest:off all"
     exec "testament html"
-
-task clean, "Remove all non-repository artifacts.":
-    exec "fossil clean -x"
+    exec """find tests/ -type f \! -name \*.nim -delete"""
 
 task docs, "Generate automated documentation.":
     exec "nim md2html --project --outdir:docs README.md"

src/kuzu.nim

@@ -13,6 +13,8 @@ else:
     include "kuzu/0.11.0.nim"
 
 import
+    std/files,
+    std/paths,
     std/strformat,
     std/strutils
 

src/kuzu/constants.nim

@@ -4,5 +4,5 @@ const KUZU_VERSION*             = "0.6.0"
 const KUZU_EXPECTED_LIBVERSION* = "0.11.0"
 const BLOB_MAXSIZE = 4096
 
-let KUZU_DEFAULT_CONFIG*  = kuzu_default_system_config()
+let KUZU_DEFAULT_CONFIG* = kuzu_default_system_config()
 

src/kuzu/database.nim

@@ -7,18 +7,50 @@ proc `=destroy`*( db: KuzuDatabaseObj ) =
         kuzu_database_destroy( addr db.handle )
 
 
-func newKuzuDatabase*( path="", config=kuzuConfig() ): KuzuDatabase =
+proc validateDatabase( db: KuzuDatabase ): void =
+    ## Perform basic validity checks against an existing on disk database
+    ## for better error messaging.
+
+    if not Path( db.path ).fileExists: return
+
+    var buf = newSeq[char]( 5 )
+    let f = open( db.path )
+    discard f.readChars( buf )
+    f.close
+
+    let magic = buf[0..3].join
+    let storage_version = buf[4].uint
+
+    if magic != "KUZU":
+        raise newException( KuzuException, "Unable to open database: " &
+            &""""{db.path}" Doesn't appear to be a Kuzu file.""" )
+
+    if storageVersion != kuzuGetStorageVersion():
+        raise newException( KuzuException, "Unable to open database: " &
+            &" mismatched storage versions - file is {storageVersion}, expected {kuzuGetStorageVersion()}." )
+
+
+proc newKuzuDatabase*( path="", config=kuzuConfig() ): KuzuDatabase =
     ## Create a new Kuzu database handle.  Creates an in-memory
     ## database by default, but writes to disk if a +path+ is supplied.
 
     result        = new KuzuDatabase
     result.config = config
-    result.path   = if path != "" and path != ":memory:": path else: "(in-memory)"
+
+    if path != "" and path != ":memory:":
+        result.path = path
+        result.kind = disk
+    else:
+        result.path = "(in-memory)"
+        result.kind = memory
+
     result.handle = kuzu_database()
 
+    if result.kind == disk:
+        result.validateDatabase()
+
     if kuzu_database_init( path, config, addr result.handle ) == KuzuSuccess:
         result.valid = true
     else:
         raise newException( KuzuException, "Unable to open database." )
 
-

src/kuzu/types.nim

@@ -1,9 +1,13 @@
 # vim: set et sta sw=4 ts=4 :
 
 type
+    KuzuDBType* = enum
+        disk, memory
+
     KuzuDatabaseObj = object
         handle:  kuzu_database
         path*:   string
+        kind*:   KuzuDBType
         config*: kuzu_system_config
         valid = false
     KuzuDatabase* = ref KuzuDatabaseObj

tests/database/t_can_create_in_memory.nim

@@ -4,4 +4,5 @@ import kuzu
 
 var db = newKuzuDatabase()
 assert db.path == "(in-memory)"
+assert db.kind == memory
 

tests/database/t_checks_for_valid_kuzu_file.nim

@@ -0,0 +1,23 @@
+# vim: set et sta sw=4 ts=4 :
+
+import
+  std/files,
+  std/paths,
+  std/re
+
+import kuzu
+
+const NOT_A_DATABASE_PATH = Path( "tmp/not-a-db" )
+
+NOT_A_DATABASE_PATH.removeFile()
+var fh = NOT_A_DATABASE_PATH.string.open( fmWrite )
+fh.write( "Hi." )
+fh.close
+
+try:
+    discard newKuzuDatabase( $NOT_A_DATABASE_PATH )
+except KuzuException as err:
+    assert err.msg.contains( re"""Unable to open database: "tmp/not-a-db" Doesn't appear to be a Kuzu file""" )
+
+NOT_A_DATABASE_PATH.removeFile()
+

tests/database/t_creates_with_default_config.nim

@@ -12,6 +12,7 @@ DATABASE_PATH.removeFile()
 var db = newKuzuDatabase( $DATABASE_PATH )
 
 assert db.path == $DATABASE_PATH
+assert db.kind == disk
 assert db.config == kuzuConfig()
 assert db.config.read_only == false