JNI doc additions.
FossilOrigin-Name: 0c7ac34f30e1f7e35a2ac4e5e55e5f24857b24afa81a7abecba60f1c9c68b9ff
This commit is contained in:
stephan
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@@ -273,8 +273,7 @@ package.jar.in := $(abspath $(dir.src)/jar.in)
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CLEAN_FILES += $(package.jar.in)
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$(package.jar.in): $(MAKEFILE) $(CLASS_FILES.main)
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cd $(dir.src); ls -1 org/sqlite/jni/*.java org/sqlite/jni/*.class > $@
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@ls -la $@
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@echo "To use this jar you will need the -Djava.library.path=DIR/WITH/libsqlite3-jni.so flag."
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@echo "To use this jar you will need the -Djava.library.path=DIR/CONTAINING/libsqlite3-jni.so flag."
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@echo "e.g. java -jar $@ -Djava.library.path=bld"
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$(package.jar): $(CLASS_FILES) $(MAKEFILE) $(package.jar.in)
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+53
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@@ -15,7 +15,10 @@ Technical support is available in the forum:
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> **FOREWARNING:** this subproject is very much in development and
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subject to any number of changes. Please do not rely on any
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information about its API until this disclaimer is removed.
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information about its API until this disclaimer is removed. The JNI
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bindgins released with version 3.43 are a "tech preview" and 3.44
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will be "final," at which point strong backward compatibility
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guarantees will apply.
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Project goals/requirements:
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@@ -40,13 +43,30 @@ Non-goals:
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- Creation of high-level OO wrapper APIs. Clients are free to create
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them off of the C-style API.
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Hello World
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-----------------------------------------------------------------------
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Significant TODOs
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========================================================================
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```java
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import org.sqlite.jni.*;
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import static org.sqlite.jni.SQLite3Jni;
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...
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OutputPointer.sqlite3 out = new OutputPointer.sqlite3();
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int rc = sqlite3_open(":memory:", out);
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final sqlite3 db = out.take();
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if( 0 != rc ){
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if( null != db ){
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System.out.print("Error opening db: "+sqlite3_errmsg(db));
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sqlite3_close(db);
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}else{
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System.out.print("Error opening db: rc="+rc);
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}
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... handle error ...
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}
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- Lots of APIs left to bind. Most "day-to-day" functionality is already
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in place and is believed to work well.
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... use db ...
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sqlite3_close_v2(db);
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```
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Building
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========================================================================
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@@ -59,55 +79,33 @@ The canonical builds assumes a Linux-like environment and requires:
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Put simply:
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```
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```console
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$ export JAVA_HOME=/path/to/jdk/root
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$ make
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$ make test
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$ make clean
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```
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The jar distribution can be created with `make jar`.
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<a id='1to1ish'></a>
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One-to-One(-ish) Mapping to C
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========================================================================
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This JNI binding aims to provide as close to a 1-to-1 experience with
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the C API as cross-language semantics allow. Exceptions are
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necessarily made where cross-language semantics do not allow a 1-to-1,
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and judiciously made where a 1-to-1 mapping would be unduly cumbersome
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to use in Java.
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the C API as cross-language semantics allow. Changes are necessarily
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made where cross-language semantics do not allow a 1-to-1, and
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judiciously made where a 1-to-1 mapping would be unduly cumbersome to
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use in Java.
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Golden Rule: _Never_ Throw from Callbacks
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Golden Rule: _Never_ Throw from Callbacks (Unless...)
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------------------------------------------------------------------------
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JNI bindings which accept client-defined functions _must never throw
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exceptions_ unless _very explicitly documented_ as being
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throw-safe. Exceptions are generally reserved for higher-level
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bindings which are constructed to specifically deal with them and
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ensure that they do not leak C-level resources. Some of the JNI
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bindings are provided as Java functions which expect this rule to
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always hold.
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UTF-8(-ish)
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------------------------------------------------------------------------
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SQLite internally uses UTF-8 encoding, whereas Java natively uses
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UTF-16. Java JNI has routines for converting to and from UTF-8, _but_
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Java uses what its docs call "[modified UTF-8][modutf8]." Care must be
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taken when converting Java strings to UTF-8 to ensure that the proper
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conversion is performed. In short,
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`String.getBytes(StandardCharsets.UTF_8)` performs the proper
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conversion in Java, and there is no JNI C API for that conversion
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(JNI's `NewStringUTF()` returns MUTF-8).
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Known consequences and limitations of this discrepancy include:
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- Names of databases, tables, and collations must not contain
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characters which differ in MUTF-8 and UTF-8, or certain APIs will
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mis-translate them on their way between languages. APIs which
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transfer other client-side data to Java take extra care to
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convert the data at the cost of performance.
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[modutf8]: https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8
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Client-defined callbacks _must never throw exceptions_ unless _very
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explicitly documented_ as being throw-safe. Exceptions are generally
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reserved for higher-level bindings which are constructed to
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specifically deal with them and ensure that they do not leak C-level
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resources.
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Unwieldy Constructs are Re-mapped
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@@ -125,7 +123,7 @@ A prime example of where interface changes for Java are necessary for
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usability is [registration of a custom
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collation](https://sqlite.org/c3ref/create_collation.html):
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```
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```c
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// C:
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int sqlite3_create_collation(sqlite3 * db, const char * name, int eTextRep,
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void *pUserData,
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@@ -144,7 +142,7 @@ passed that object as their first argument. That data is passed around
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bind that part as-is to Java, the result would be awkward to use (^Yes,
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we tried this.):
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```
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```java
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// Java:
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int sqlite3_create_collation(sqlite3 db, String name, int eTextRep,
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Object pUserData, xCompareType xCompare);
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@@ -159,7 +157,7 @@ for callbacks and (B) having their internal state provided separately,
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which is ill-fitting in Java. For the sake of usability, C APIs which
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follow that pattern use a slightly different Java interface:
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```
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```java
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int sqlite3_create_collation(sqlite3 db, String name, int eTextRep,
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Collation collation);
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```
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@@ -168,7 +166,7 @@ Where the `Collation` class has an abstract `xCompare()` method and
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no-op `xDestroy()` method which can be overridden if needed, leading to
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a much more Java-esque usage:
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```
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```java
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int rc = sqlite3_create_collation(db, "mycollation", SQLITE_UTF8, new Collation(){
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// Required comparison function:
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@@ -187,8 +185,8 @@ int rc = sqlite3_create_collation(db, "mycollation", SQLITE_UTF8, new Collation(
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Noting that:
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- It is still possible to bind in call-scope-local state via closures,
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if desired.
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- It is possible to bind in call-scope-local state via closures, if
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desired, as opposed to packing it into the Collation object.
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- No capabilities of the C API are lost or unduly obscured via the
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above API reshaping, so power users need not make any compromises.
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@@ -199,6 +197,7 @@ Noting that:
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overriding the `xDestroy()` method effectively gives it v2
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semantics.
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### User-defined SQL Functions (a.k.a. UDFs)
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The [`sqlite3_create_function()`](https://sqlite.org/c3ref/create_function.html)
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@@ -206,12 +205,13 @@ family of APIs make heavy use of function pointers to provide
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client-defined callbacks, necessitating interface changes in the JNI
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binding. The Java API has only one core function-registration function:
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```
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```java
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int sqlite3_create_function(sqlite3 db, String funcName, int nArgs,
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int encoding, SQLFunction func);
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```
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> Design question: does the encoding argument serve any purpose in JS?
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> Design question: does the encoding argument serve any purpose in
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Java? That's as-yet undetermined. If not, it will be removed.
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`SQLFunction` is not used directly, but is instead instantiated via
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one of its three subclasses:
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@@ -229,5 +229,8 @@ Search [`Tester1.java`](/file/ext/jni/src/org/sqlite/jni/Tester1.java) for
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Reminder: see the disclaimer at the top of this document regarding the
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in-flux nature of this API.
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[jsrc]: /file/
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[www]: https://sqlite.org
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### And so on...
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Various APIs which accept callbacks, e.g. `sqlite3_trace_v2()` and
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`sqlite3_update_hook()`, use interfaces similar to those shown above.
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@@ -1,5 +1,5 @@
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C JNI\stest\scode\scleanups.
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D 2023-08-19T11:52:36.349
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C JNI\sdoc\sadditions.
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D 2023-08-19T12:32:00.131
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F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
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F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
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F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
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@@ -231,8 +231,8 @@ F ext/fts5/tool/showfts5.tcl d54da0e067306663e2d5d523965ca487698e722c
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F ext/icu/README.txt 7ab7ced8ae78e3a645b57e78570ff589d4c672b71370f5aa9e1cd7024f400fc9
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F ext/icu/icu.c c074519b46baa484bb5396c7e01e051034da8884bad1a1cb7f09bbe6be3f0282
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F ext/icu/sqliteicu.h fa373836ed5a1ee7478bdf8a1650689294e41d0c89c1daab26e9ae78a32075a8
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F ext/jni/GNUmakefile 4217266579b74499708d0b9fd7de598d67cc1992646518596ec83f134c3e2d85
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F ext/jni/README.md 7a614a2fa6c561205f7a53fd8626cf93a7b5711ff454fc1814517f796df398eb
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F ext/jni/GNUmakefile ace719d6d7025a0a454b7c661de2beef9a0e819535ad0ce0742034da8ff8d27f
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F ext/jni/README.md 975b35173debbbf3a4ab7166e14d2ffa2bacff9b6850414f09cc919805e81ba4
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F ext/jni/jar-dist.make 9a03d10dbb5a74c724bfec4b76fd9e4c9865cbbc858d731cb48f38ac897d73a3
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F ext/jni/src/c/sqlite3-jni.c 8608cb36223d6bc64e8ddd9296b6d63a4fc54efaf8dbc3ea7e5eca81f4801d42
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F ext/jni/src/c/sqlite3-jni.h f10d2f38720687c70ecdd5e44f6e8db98efee2caa05fc86b2d9e0c76e6cc0a18
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@@ -2091,8 +2091,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
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F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
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F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
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R 109361c70c87f2804d75b9c237ee841f
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U stephan
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Z a181fae7a989c6647ffb5b92efaaa712
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Z 56d27110aeccda606f4b75566f7a0870
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# Remove this line to create a well-formed Fossil manifest.
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+1
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@@ -1 +1 @@
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e202b6e69da8cced114d027cf2e91a04dfdd50b601b3274214783f7d750c558c
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0c7ac34f30e1f7e35a2ac4e5e55e5f24857b24afa81a7abecba60f1c9c68b9ff
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